diff --git a/backend/Application/Abstractions/IdeaContracts.cs b/backend/Application/Abstractions/IdeaContracts.cs
new file mode 100644
index 0000000..169f420
--- /dev/null
+++ b/backend/Application/Abstractions/IdeaContracts.cs
@@ -0,0 +1,59 @@
+using TarninaHub.Application.Dtos;
+
+namespace TarninaHub.Application.Abstractions;
+
+public interface IIdeaService
+{
+    Task<IdeaResponse> CreateAsync(string authorId, CreateIdeaRequest request, CancellationToken cancellationToken);
+
+    Task<IdeaResponse?> GetAsync(string ideaId, CancellationToken cancellationToken);
+
+    Task<IReadOnlyList<IdeaResponse>> ListForAuthorAsync(string authorId, CancellationToken cancellationToken);
+
+    Task<IdeaResponse?> UpdateAsync(string ideaId, UpdateIdeaRequest request, CancellationToken cancellationToken);
+
+    Task<IdeaCardResponse?> GetCardAsync(string ideaId, CancellationToken cancellationToken);
+
+    Task<IdeaCardResponse?> UpdateCardAsync(string ideaId, IdeaCardRequest request, CancellationToken cancellationToken);
+}
+
+public interface IIdeaAssistant
+{
+    Task<IdeaAssistResponse?> AssistAsync(
+        string ideaId,
+        IdeaAssistRequest request,
+        CancellationToken cancellationToken);
+}
+
+public interface IGrantCallService
+{
+    Task<IReadOnlyList<GrantCallResponse>> ListAsync(string? status, CancellationToken cancellationToken);
+
+    Task<GrantCallResponse?> GetAsync(string grantCallId, CancellationToken cancellationToken);
+}
+
+public enum CreateApplicationOutcome
+{
+    Created,
+    CallNotFound,
+    CallNotOpen,
+    IdeaNotFound,
+}
+
+public sealed record CreateApplicationResult(
+    CreateApplicationOutcome Outcome,
+    ApplicationResponse? Application);
+
+public interface IApplicationService
+{
+    Task<CreateApplicationResult> CreateAsync(
+        string userId,
+        CreateApplicationRequest request,
+        CancellationToken cancellationToken);
+
+    Task<ApplicationResponse?> GetAsync(string applicationId, CancellationToken cancellationToken);
+
+    Task<IReadOnlyList<ApplicationResponse>> ListForAuthorAsync(
+        string authorId,
+        CancellationToken cancellationToken);
+}
diff --git a/backend/Application/Dtos/ApplicationDtos.cs b/backend/Application/Dtos/ApplicationDtos.cs
new file mode 100644
index 0000000..59c701a
--- /dev/null
+++ b/backend/Application/Dtos/ApplicationDtos.cs
@@ -0,0 +1,28 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace TarninaHub.Application.Dtos;
+
+public sealed record GrantCallResponse(
+    string Id,
+    string Name,
+    DateTimeOffset OpensAt,
+    DateTimeOffset ClosesAt,
+    string Status,
+    string? ExternalId);
+
+public sealed record CreateApplicationRequest(
+    [Required] string GrantCallId,
+    [Required] string IdeaId,
+    IReadOnlyDictionary<string, object?>? Content);
+
+public sealed record UpdateApplicationRequest(
+    IReadOnlyDictionary<string, object?>? Content,
+    string? Status);
+
+public sealed record ApplicationResponse(
+    string Id,
+    string GrantCallId,
+    string IdeaId,
+    IReadOnlyDictionary<string, object?> Content,
+    string Status,
+    DateTimeOffset CreatedAt);
diff --git a/backend/Application/Dtos/IdeaDtos.cs b/backend/Application/Dtos/IdeaDtos.cs
new file mode 100644
index 0000000..81601f7
--- /dev/null
+++ b/backend/Application/Dtos/IdeaDtos.cs
@@ -0,0 +1,41 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace TarninaHub.Application.Dtos;
+
+public sealed record IdeaCardRequest(
+    string? Essence,
+    string? Audience,
+    string? Stage);
+
+public sealed record CreateIdeaRequest(
+    [Required, StringLength(200, MinimumLength = 3)] string Title,
+    [Required, StringLength(4000, MinimumLength = 10)] string Description,
+    IdeaCardRequest? Card);
+
+public sealed record UpdateIdeaRequest(
+    [Required, StringLength(200, MinimumLength = 3)] string Title,
+    [Required, StringLength(4000, MinimumLength = 10)] string Description,
+    string? Status);
+
+public sealed record IdeaCardResponse(
+    string Id,
+    string IdeaId,
+    string Essence,
+    string Audience,
+    string Stage);
+
+public sealed record IdeaResponse(
+    string Id,
+    string Title,
+    string Description,
+    string AuthorId,
+    string Status,
+    IdeaCardResponse? Card,
+    DateTimeOffset? UpdatedAt);
+
+public sealed record IdeaAssistRequest(string? Focus);
+
+public sealed record IdeaAssistResponse(
+    IReadOnlyList<string> Suggestions,
+    string ImprovedDescription,
+    bool FromLlm);
diff --git a/backend/Application/Mappings/IdeaStatusWire.cs b/backend/Application/Mappings/IdeaStatusWire.cs
new file mode 100644
index 0000000..a97c6af
--- /dev/null
+++ b/backend/Application/Mappings/IdeaStatusWire.cs
@@ -0,0 +1,26 @@
+using TarninaHub.Domain.Enums;
+
+namespace TarninaHub.Application.Mappings;
+
+public static class IdeaStatusWire
+{
+    public static string ToWire(this IdeaStatus status) => status switch
+    {
+        IdeaStatus.Draft => "draft",
+        IdeaStatus.Submitted => "submitted",
+        IdeaStatus.InReview => "in_review",
+        IdeaStatus.Accepted => "accepted",
+        IdeaStatus.Rejected => "rejected",
+        _ => throw new ArgumentOutOfRangeException(nameof(status), status, null),
+    };
+
+    public static IdeaStatus? Parse(string? value) => value switch
+    {
+        "draft" => IdeaStatus.Draft,
+        "submitted" => IdeaStatus.Submitted,
+        "in_review" => IdeaStatus.InReview,
+        "accepted" => IdeaStatus.Accepted,
+        "rejected" => IdeaStatus.Rejected,
+        _ => null,
+    };
+}
diff --git a/backend/Controllers/ApplicationsController.cs b/backend/Controllers/ApplicationsController.cs
new file mode 100644
index 0000000..2bc2d0e
--- /dev/null
+++ b/backend/Controllers/ApplicationsController.cs
@@ -0,0 +1,104 @@
+using Asp.Versioning;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+using TarninaHub.Application.Security;
+
+namespace TarninaHub.Controllers;
+
+[ApiController]
+[ApiVersion("1.0")]
+[Route("api/applications")]
+[Authorize]
+public class ApplicationsController : ControllerBase
+{
+    private readonly IApplicationService _applicationService;
+    private readonly IIdeaService _ideaService;
+
+    public ApplicationsController(IApplicationService applicationService, IIdeaService ideaService)
+    {
+        _applicationService = applicationService;
+        _ideaService = ideaService;
+    }
+
+    [HttpPost]
+    public async Task<ActionResult<ApplicationResponse>> Create(
+        CreateApplicationRequest request,
+        CancellationToken cancellationToken)
+    {
+        var userId = User.GetUserId();
+
+        if (string.IsNullOrWhiteSpace(userId))
+        {
+            return Unauthorized();
+        }
+
+        var result = await _applicationService.CreateAsync(userId, request, cancellationToken);
+
+        return result.Outcome switch
+        {
+            CreateApplicationOutcome.Created when result.Application is not null =>
+                CreatedAtAction(nameof(GetById), new { applicationId = result.Application.Id }, result.Application),
+            CreateApplicationOutcome.CallNotFound => NotFound(new ProblemDetails
+            {
+                Title = "Grant call not found",
+                Status = StatusCodes.Status404NotFound,
+            }),
+            CreateApplicationOutcome.IdeaNotFound => NotFound(new ProblemDetails
+            {
+                Title = "Idea not found",
+                Status = StatusCodes.Status404NotFound,
+            }),
+            _ => Conflict(new ProblemDetails
+            {
+                Title = "Grant call is not open",
+                Detail = "Applications are only accepted while the call is open and within its window.",
+                Status = StatusCodes.Status409Conflict,
+            }),
+        };
+    }
+
+    [HttpGet]
+    public async Task<ActionResult<IReadOnlyList<ApplicationResponse>>> ListMine(CancellationToken cancellationToken)
+    {
+        var userId = User.GetUserId();
+
+        if (string.IsNullOrWhiteSpace(userId))
+        {
+            return Unauthorized();
+        }
+
+        var applications = await _applicationService.ListForAuthorAsync(userId, cancellationToken);
+
+        return Ok(applications);
+    }
+
+    [HttpGet("{applicationId}")]
+    public async Task<ActionResult<ApplicationResponse>> GetById(
+        string applicationId,
+        CancellationToken cancellationToken)
+    {
+        var application = await _applicationService.GetAsync(applicationId, cancellationToken);
+
+        if (application is null)
+        {
+            return NotFound();
+        }
+
+        if (!IsStaff())
+        {
+            var idea = await _ideaService.GetAsync(application.IdeaId, cancellationToken);
+
+            if (idea is null || !string.Equals(idea.AuthorId, User.GetUserId(), StringComparison.Ordinal))
+            {
+                return Forbid();
+            }
+        }
+
+        return Ok(application);
+    }
+
+    private bool IsStaff() =>
+        User.IsInRole(RoleNames.Operator) || User.IsInRole(RoleNames.Manager) || User.IsInRole(RoleNames.Admin);
+}
diff --git a/backend/Controllers/GrantCallsController.cs b/backend/Controllers/GrantCallsController.cs
new file mode 100644
index 0000000..c3fe992
--- /dev/null
+++ b/backend/Controllers/GrantCallsController.cs
@@ -0,0 +1,41 @@
+using Asp.Versioning;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+
+namespace TarninaHub.Controllers;
+
+[ApiController]
+[ApiVersion("1.0")]
+[Route("api/grant-calls")]
+[Authorize]
+public class GrantCallsController : ControllerBase
+{
+    private readonly IGrantCallService _grantCalls;
+
+    public GrantCallsController(IGrantCallService grantCalls)
+    {
+        _grantCalls = grantCalls;
+    }
+
+    [HttpGet]
+    public async Task<ActionResult<IReadOnlyList<GrantCallResponse>>> List(
+        [FromQuery] string? status,
+        CancellationToken cancellationToken)
+    {
+        var calls = await _grantCalls.ListAsync(status, cancellationToken);
+
+        return Ok(calls);
+    }
+
+    [HttpGet("{grantCallId}")]
+    public async Task<ActionResult<GrantCallResponse>> GetById(
+        string grantCallId,
+        CancellationToken cancellationToken)
+    {
+        var call = await _grantCalls.GetAsync(grantCallId, cancellationToken);
+
+        return call is null ? NotFound() : Ok(call);
+    }
+}
diff --git a/backend/Controllers/IdeasController.cs b/backend/Controllers/IdeasController.cs
new file mode 100644
index 0000000..dc1007d
--- /dev/null
+++ b/backend/Controllers/IdeasController.cs
@@ -0,0 +1,186 @@
+using Asp.Versioning;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+using TarninaHub.Application.Mappings;
+using TarninaHub.Application.Security;
+using TarninaHub.Domain.Rules;
+
+namespace TarninaHub.Controllers;
+
+[ApiController]
+[ApiVersion("1.0")]
+[Route("api/ideas")]
+[Authorize]
+public class IdeasController : ControllerBase
+{
+    private readonly IIdeaService _ideaService;
+    private readonly IIdeaAssistant _ideaAssistant;
+
+    public IdeasController(IIdeaService ideaService, IIdeaAssistant ideaAssistant)
+    {
+        _ideaService = ideaService;
+        _ideaAssistant = ideaAssistant;
+    }
+
+    [HttpPost]
+    public async Task<ActionResult<IdeaResponse>> Create(
+        CreateIdeaRequest request,
+        CancellationToken cancellationToken)
+    {
+        var userId = User.GetUserId();
+
+        if (string.IsNullOrWhiteSpace(userId))
+        {
+            return Unauthorized();
+        }
+
+        var created = await _ideaService.CreateAsync(userId, request, cancellationToken);
+
+        return CreatedAtAction(nameof(GetById), new { ideaId = created.Id }, created);
+    }
+
+    [HttpGet]
+    public async Task<ActionResult<IReadOnlyList<IdeaResponse>>> ListMine(CancellationToken cancellationToken)
+    {
+        var userId = User.GetUserId();
+
+        if (string.IsNullOrWhiteSpace(userId))
+        {
+            return Unauthorized();
+        }
+
+        var ideas = await _ideaService.ListForAuthorAsync(userId, cancellationToken);
+
+        return Ok(ideas);
+    }
+
+    [HttpGet("{ideaId}")]
+    public async Task<ActionResult<IdeaResponse>> GetById(string ideaId, CancellationToken cancellationToken)
+    {
+        var idea = await _ideaService.GetAsync(ideaId, cancellationToken);
+
+        if (idea is null)
+        {
+            return NotFound();
+        }
+
+        if (!IsOwner(idea) && !IsStaff())
+        {
+            return Forbid();
+        }
+
+        return Ok(idea);
+    }
+
+    [HttpPut("{ideaId}")]
+    public async Task<ActionResult<IdeaResponse>> Update(
+        string ideaId,
+        UpdateIdeaRequest request,
+        CancellationToken cancellationToken)
+    {
+        var current = await _ideaService.GetAsync(ideaId, cancellationToken);
+
+        if (current is null)
+        {
+            return NotFound();
+        }
+
+        if (!IsOwner(current))
+        {
+            return Forbid();
+        }
+
+        if (!string.IsNullOrWhiteSpace(request.Status))
+        {
+            var from = IdeaStatusWire.Parse(current.Status);
+            var to = IdeaStatusWire.Parse(request.Status);
+
+            if (to is null || from is null || !IdeaWorkflow.CanTransition(from.Value, to.Value))
+            {
+                ModelState.AddModelError(
+                    nameof(request.Status),
+                    $"Transition from '{current.Status}' to '{request.Status}' is not allowed.");
+
+                return ValidationProblem(ModelState);
+            }
+        }
+
+        var updated = await _ideaService.UpdateAsync(ideaId, request, cancellationToken);
+
+        return updated is null ? NotFound() : Ok(updated);
+    }
+
+    [HttpGet("{ideaId}/card")]
+    public async Task<ActionResult<IdeaCardResponse>> GetCard(string ideaId, CancellationToken cancellationToken)
+    {
+        var idea = await _ideaService.GetAsync(ideaId, cancellationToken);
+
+        if (idea is null)
+        {
+            return NotFound();
+        }
+
+        if (!IsOwner(idea) && !IsStaff())
+        {
+            return Forbid();
+        }
+
+        var card = await _ideaService.GetCardAsync(ideaId, cancellationToken);
+
+        return card is null ? NotFound() : Ok(card);
+    }
+
+    [HttpPut("{ideaId}/card")]
+    public async Task<ActionResult<IdeaCardResponse>> UpdateCard(
+        string ideaId,
+        IdeaCardRequest request,
+        CancellationToken cancellationToken)
+    {
+        var idea = await _ideaService.GetAsync(ideaId, cancellationToken);
+
+        if (idea is null)
+        {
+            return NotFound();
+        }
+
+        if (!IsOwner(idea))
+        {
+            return Forbid();
+        }
+
+        var card = await _ideaService.UpdateCardAsync(ideaId, request, cancellationToken);
+
+        return card is null ? NotFound() : Ok(card);
+    }
+
+    [HttpPost("{ideaId}/assist")]
+    public async Task<ActionResult<IdeaAssistResponse>> Assist(
+        string ideaId,
+        IdeaAssistRequest request,
+        CancellationToken cancellationToken)
+    {
+        var idea = await _ideaService.GetAsync(ideaId, cancellationToken);
+
+        if (idea is null)
+        {
+            return NotFound();
+        }
+
+        if (!IsOwner(idea) && !IsStaff())
+        {
+            return Forbid();
+        }
+
+        var assist = await _ideaAssistant.AssistAsync(ideaId, request, cancellationToken);
+
+        return assist is null ? NotFound() : Ok(assist);
+    }
+
+    private bool IsOwner(IdeaResponse idea) =>
+        string.Equals(idea.AuthorId, User.GetUserId(), StringComparison.Ordinal);
+
+    private bool IsStaff() =>
+        User.IsInRole(RoleNames.Operator) || User.IsInRole(RoleNames.Manager) || User.IsInRole(RoleNames.Admin);
+}
diff --git a/backend/Domain/Rules/ApplicationWindow.cs b/backend/Domain/Rules/ApplicationWindow.cs
new file mode 100644
index 0000000..eecc074
--- /dev/null
+++ b/backend/Domain/Rules/ApplicationWindow.cs
@@ -0,0 +1,13 @@
+namespace TarninaHub.Domain.Rules;
+
+public static class ApplicationWindow
+{
+    public const string Open = "open";
+
+    /// <summary>
+    /// Applications are only allowed while the call is open and the current
+    /// moment is within [opensAt, closesAt].
+    /// </summary>
+    public static bool IsOpen(string status, DateTimeOffset opensAt, DateTimeOffset closesAt, DateTimeOffset now) =>
+        string.Equals(status, Open, StringComparison.Ordinal) && now >= opensAt && now <= closesAt;
+}
diff --git a/backend/Domain/Rules/IdeaWorkflow.cs b/backend/Domain/Rules/IdeaWorkflow.cs
new file mode 100644
index 0000000..d8fb19c
--- /dev/null
+++ b/backend/Domain/Rules/IdeaWorkflow.cs
@@ -0,0 +1,22 @@
+using TarninaHub.Domain.Enums;
+
+namespace TarninaHub.Domain.Rules;
+
+public static class IdeaWorkflow
+{
+    private static readonly IReadOnlyDictionary<IdeaStatus, IdeaStatus[]> Transitions =
+        new Dictionary<IdeaStatus, IdeaStatus[]>
+        {
+            [IdeaStatus.Draft] = [IdeaStatus.Submitted],
+            [IdeaStatus.Submitted] = [IdeaStatus.InReview],
+            [IdeaStatus.InReview] = [IdeaStatus.Accepted, IdeaStatus.Rejected],
+            [IdeaStatus.Accepted] = [],
+            [IdeaStatus.Rejected] = [],
+        };
+
+    public static bool CanTransition(IdeaStatus from, IdeaStatus to) =>
+        from == to || Transitions[from].Contains(to);
+
+    public static bool IsTerminal(IdeaStatus status) =>
+        Transitions[status].Length == 0;
+}
diff --git a/backend/Infrastructure/Assist/IdeaAssistant.cs b/backend/Infrastructure/Assist/IdeaAssistant.cs
new file mode 100644
index 0000000..fd748a4
--- /dev/null
+++ b/backend/Infrastructure/Assist/IdeaAssistant.cs
@@ -0,0 +1,87 @@
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+using TarninaHub.Application.Matchmaking;
+
+namespace TarninaHub.Infrastructure.Assist;
+
+/// <summary>
+/// Idea-creator assistant. Uses the configured LLM when available and falls
+/// back to deterministic, stage-aware suggestions otherwise.
+/// </summary>
+public sealed class IdeaAssistant : IIdeaAssistant
+{
+    private const string SystemPrompt =
+        "Jesteś asystentem kreatora innowacji społecznych w Małopolskim Hubie Innowacji Społecznych. " +
+        "Rozwijasz pomysł mieszkańca: podajesz konkretne, praktyczne podpowiedzi prostym językiem. " +
+        "Nie wymyślaj faktów ani danych liczbowych.";
+
+    private readonly IIdeaService _ideaService;
+    private readonly ILlmProvider _llmProvider;
+    private readonly ILlmRequestLimiter _llmRequestLimiter;
+
+    public IdeaAssistant(
+        IIdeaService ideaService,
+        ILlmProvider llmProvider,
+        ILlmRequestLimiter llmRequestLimiter)
+    {
+        _ideaService = ideaService;
+        _llmProvider = llmProvider;
+        _llmRequestLimiter = llmRequestLimiter;
+    }
+
+    public async Task<IdeaAssistResponse?> AssistAsync(
+        string ideaId,
+        IdeaAssistRequest request,
+        CancellationToken cancellationToken)
+    {
+        var idea = await _ideaService.GetAsync(ideaId, cancellationToken);
+
+        if (idea is null)
+        {
+            return null;
+        }
+
+        var improvedDescription = idea.Description;
+        var fromLlm = false;
+
+        if (_llmProvider.IsConfigured && _llmRequestLimiter.TryAcquire())
+        {
+            var userPrompt =
+                $"Pomysł: {idea.Title}\n" +
+                $"Opis: {idea.Description}\n" +
+                $"Etap: {idea.Card?.Stage ?? "idea"}\n" +
+                $"Odbiorca: {idea.Card?.Audience ?? "nieokreślony"}\n" +
+                $"Fokus: {request.Focus ?? "ogólny"}\n" +
+                "Rozwiń opis pomysłu i dodaj praktyczne wskazówki.";
+
+            var completion = await _llmProvider.CompleteAsync(SystemPrompt, userPrompt, cancellationToken);
+
+            if (!string.IsNullOrWhiteSpace(completion))
+            {
+                improvedDescription = completion.Trim();
+                fromLlm = true;
+            }
+        }
+
+        return new IdeaAssistResponse(BuildSuggestions(idea), improvedDescription, fromLlm);
+    }
+
+    private static IReadOnlyList<string> BuildSuggestions(IdeaResponse idea)
+    {
+        var stage = idea.Card?.Stage ?? "idea";
+        var suggestions = new List<string>
+        {
+            "Doprecyzuj grupę docelową i jej konkretną potrzebę.",
+            "Określ, jak zmierzysz efekt (wskaźniki, liczba odbiorców).",
+            "Zaplanuj mały pilotaż i wskaż partnerów (NGO/JST/firma).",
+            $"Dopasuj opis do etapu '{stage}' i sprawdź wymagania naboru.",
+        };
+
+        if (!string.IsNullOrWhiteSpace(idea.Card?.Audience))
+        {
+            suggestions.Add($"Rozwiń opis odbiorcy: {idea.Card.Audience}.");
+        }
+
+        return suggestions;
+    }
+}
diff --git a/backend/Infrastructure/DependencyInjection.cs b/backend/Infrastructure/DependencyInjection.cs
index 5f6924b..fbb736c 100644
--- a/backend/Infrastructure/DependencyInjection.cs
+++ b/backend/Infrastructure/DependencyInjection.cs
@@ -4,6 +4,7 @@ using SurrealDb.Net;
 using TarninaHub.Application.Abstractions;
 using TarninaHub.Application.Matchmaking;
 using TarninaHub.Infrastructure.Auth;
+using TarninaHub.Infrastructure.Assist;
 using TarninaHub.Infrastructure.Events;
 using TarninaHub.Infrastructure.Llm;
 using TarninaHub.Infrastructure.Persistence;
@@ -80,6 +81,10 @@ public static class DependencyInjection
         services.AddSingleton<ITrendService, TrendService>();
         services.AddSingleton<IEmbeddingProvider, HashingEmbeddingProvider>();
         services.AddSingleton<IMatchmakingService, MatchmakingService>();
+        services.AddSingleton<IIdeaService, IdeaService>();
+        services.AddSingleton<IGrantCallService, GrantCallService>();
+        services.AddSingleton<IApplicationService, ApplicationService>();
+        services.AddSingleton<IIdeaAssistant, IdeaAssistant>();
 
         return services;
     }
diff --git a/backend/Infrastructure/Persistence/ApplicationService.cs b/backend/Infrastructure/Persistence/ApplicationService.cs
new file mode 100644
index 0000000..de808ae
--- /dev/null
+++ b/backend/Infrastructure/Persistence/ApplicationService.cs
@@ -0,0 +1,136 @@
+using SurrealDb.Net;
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+using TarninaHub.Domain.Rules;
+
+namespace TarninaHub.Infrastructure.Persistence;
+
+public sealed class ApplicationService : IApplicationService
+{
+    private const string SelectFields =
+        "type::string(id) AS id, type::string(grant_call) AS grant_call, type::string(idea) AS idea, " +
+        "content, status, created_at";
+
+    private readonly ISurrealDbClient _client;
+    private readonly IGrantCallService _grantCallService;
+    private readonly IIdeaService _ideaService;
+
+    public ApplicationService(
+        ISurrealDbClient client,
+        IGrantCallService grantCallService,
+        IIdeaService ideaService)
+    {
+        _client = client;
+        _grantCallService = grantCallService;
+        _ideaService = ideaService;
+    }
+
+    public async Task<CreateApplicationResult> CreateAsync(
+        string userId,
+        CreateApplicationRequest request,
+        CancellationToken cancellationToken)
+    {
+        var grantCall = await _grantCallService.GetAsync(request.GrantCallId, cancellationToken);
+
+        if (grantCall is null)
+        {
+            return new CreateApplicationResult(CreateApplicationOutcome.CallNotFound, null);
+        }
+
+        if (!ApplicationWindow.IsOpen(grantCall.Status, grantCall.OpensAt, grantCall.ClosesAt, DateTimeOffset.UtcNow))
+        {
+            return new CreateApplicationResult(CreateApplicationOutcome.CallNotOpen, null);
+        }
+
+        var idea = await _ideaService.GetAsync(request.IdeaId, cancellationToken);
+
+        if (idea is null)
+        {
+            return new CreateApplicationResult(CreateApplicationOutcome.IdeaNotFound, null);
+        }
+
+        var id = Guid.NewGuid().ToString("N");
+        var (grantTable, grantId) = SurrealRecordId.Split(request.GrantCallId);
+        var (ideaTable, ideaIdPart) = SurrealRecordId.Split(request.IdeaId);
+
+        var response = await _client.RawQuery(
+            "CREATE type::record('application', $id) SET " +
+            "grant_call = type::record($grantTable, $grantId), " +
+            "idea = type::record($ideaTable, $ideaId), " +
+            "content = $content, status = 'draft'; " +
+            $"SELECT {SelectFields} FROM type::record('application', $id) LIMIT 1;",
+            new Dictionary<string, object?>
+            {
+                ["id"] = id,
+                ["grantTable"] = grantTable,
+                ["grantId"] = grantId,
+                ["ideaTable"] = ideaTable,
+                ["ideaId"] = ideaIdPart,
+                ["content"] = ToStorageContent(request.Content),
+            },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<ApplicationRow>>(1) ?? [];
+
+        return new CreateApplicationResult(CreateApplicationOutcome.Created, Map(rows[0]));
+    }
+
+    public async Task<ApplicationResponse?> GetAsync(string applicationId, CancellationToken cancellationToken)
+    {
+        var (table, id) = SurrealRecordId.Split(applicationId);
+
+        var response = await _client.RawQuery(
+            $"SELECT {SelectFields} FROM type::record($table, $id) LIMIT 1;",
+            new Dictionary<string, object?> { ["table"] = table, ["id"] = id },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<ApplicationRow>>(0) ?? [];
+
+        return rows.Count > 0 ? Map(rows[0]) : null;
+    }
+
+    public async Task<IReadOnlyList<ApplicationResponse>> ListForAuthorAsync(
+        string authorId,
+        CancellationToken cancellationToken)
+    {
+        var (table, id) = SurrealRecordId.Split(authorId);
+
+        var response = await _client.RawQuery(
+            $"SELECT {SelectFields} FROM application WHERE idea.author = type::record($table, $id) " +
+            "ORDER BY created_at DESC;",
+            new Dictionary<string, object?> { ["table"] = table, ["id"] = id },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<ApplicationRow>>(0) ?? [];
+
+        return rows.Select(Map).ToList();
+    }
+
+    private static ApplicationResponse Map(ApplicationRow row) => new(
+        row.Id,
+        row.GrantCall,
+        row.Idea,
+        row.Content.ToDictionary(pair => pair.Key, pair => (object?)pair.Value),
+        row.Status,
+        row.CreatedAt);
+
+    private static Dictionary<string, string?> ToStorageContent(IReadOnlyDictionary<string, object?>? content)
+    {
+        var result = new Dictionary<string, string?>();
+
+        if (content is null)
+        {
+            return result;
+        }
+
+        foreach (var (key, value) in content)
+        {
+            result[key] = value?.ToString();
+        }
+
+        return result;
+    }
+}
diff --git a/backend/Infrastructure/Persistence/GrantCallService.cs b/backend/Infrastructure/Persistence/GrantCallService.cs
new file mode 100644
index 0000000..3d85f8e
--- /dev/null
+++ b/backend/Infrastructure/Persistence/GrantCallService.cs
@@ -0,0 +1,65 @@
+using SurrealDb.Net;
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+
+namespace TarninaHub.Infrastructure.Persistence;
+
+public sealed class GrantCallService : IGrantCallService
+{
+    private const string SelectFields =
+        "type::string(id) AS id, name, opens_at, closes_at, status, external_id";
+
+    private readonly ISurrealDbClient _client;
+
+    public GrantCallService(ISurrealDbClient client)
+    {
+        _client = client;
+    }
+
+    public async Task<IReadOnlyList<GrantCallResponse>> ListAsync(
+        string? status,
+        CancellationToken cancellationToken)
+    {
+        var parameters = new Dictionary<string, object?>();
+        var where = string.Empty;
+
+        if (!string.IsNullOrWhiteSpace(status))
+        {
+            where = " WHERE status = $status";
+            parameters["status"] = status;
+        }
+
+        var response = await _client.RawQuery(
+            $"SELECT {SelectFields} FROM grant_call{where} ORDER BY opens_at DESC;",
+            parameters,
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<GrantCallRow>>(0) ?? [];
+
+        return rows.Select(Map).ToList();
+    }
+
+    public async Task<GrantCallResponse?> GetAsync(string grantCallId, CancellationToken cancellationToken)
+    {
+        var (table, id) = SurrealRecordId.Split(grantCallId);
+
+        var response = await _client.RawQuery(
+            $"SELECT {SelectFields} FROM type::record($table, $id) LIMIT 1;",
+            new Dictionary<string, object?> { ["table"] = table, ["id"] = id },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<GrantCallRow>>(0) ?? [];
+
+        return rows.Count > 0 ? Map(rows[0]) : null;
+    }
+
+    private static GrantCallResponse Map(GrantCallRow row) => new(
+        row.Id,
+        row.Name,
+        row.OpensAt,
+        row.ClosesAt,
+        row.Status,
+        row.ExternalId);
+}
diff --git a/backend/Infrastructure/Persistence/IdeaService.cs b/backend/Infrastructure/Persistence/IdeaService.cs
new file mode 100644
index 0000000..2f7ce5e
--- /dev/null
+++ b/backend/Infrastructure/Persistence/IdeaService.cs
@@ -0,0 +1,218 @@
+using SurrealDb.Net;
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+using TarninaHub.Application.Mappings;
+
+namespace TarninaHub.Infrastructure.Persistence;
+
+public sealed class IdeaService : IIdeaService
+{
+    private const string SelectIdeaFields =
+        "type::string(id) AS id, title, description, type::string(author) AS author, status, updated_at";
+
+    private const string SelectCardFields =
+        "type::string(id) AS id, type::string(idea) AS idea, essence, audience, stage";
+
+    private readonly ISurrealDbClient _client;
+
+    public IdeaService(ISurrealDbClient client)
+    {
+        _client = client;
+    }
+
+    public async Task<IdeaResponse> CreateAsync(
+        string authorId,
+        CreateIdeaRequest request,
+        CancellationToken cancellationToken)
+    {
+        var ideaId = Guid.NewGuid().ToString("N");
+        var cardId = Guid.NewGuid().ToString("N");
+        var (authorTable, authorIdPart) = SurrealRecordId.Split(authorId);
+        var card = request.Card ?? new IdeaCardRequest(null, null, null);
+
+        var ideaResponse = await _client.RawQuery(
+            "CREATE type::record('idea', $id) SET title = $title, description = $description, " +
+            "author = type::record($authorTable, $authorId), status = 'draft';",
+            new Dictionary<string, object?>
+            {
+                ["id"] = ideaId,
+                ["title"] = request.Title,
+                ["description"] = request.Description,
+                ["authorTable"] = authorTable,
+                ["authorId"] = authorIdPart,
+            },
+            cancellationToken);
+        ideaResponse.EnsureAllOks();
+
+        var cardResponse = await _client.RawQuery(
+            "CREATE type::record('idea_card', $id) SET idea = type::record('idea', $ideaId), " +
+            "essence = $essence, audience = $audience, stage = $stage;",
+            new Dictionary<string, object?>
+            {
+                ["id"] = cardId,
+                ["ideaId"] = ideaId,
+                ["essence"] = card.Essence ?? string.Empty,
+                ["audience"] = card.Audience ?? string.Empty,
+                ["stage"] = string.IsNullOrWhiteSpace(card.Stage) ? "idea" : card.Stage,
+            },
+            cancellationToken);
+        cardResponse.EnsureAllOks();
+
+        return await LoadAsync($"idea:{ideaId}", cancellationToken)
+            ?? throw new InvalidOperationException("Idea could not be loaded after creation.");
+    }
+
+    public async Task<IdeaResponse?> GetAsync(string ideaId, CancellationToken cancellationToken) =>
+        await LoadAsync(ideaId, cancellationToken);
+
+    public async Task<IReadOnlyList<IdeaResponse>> ListForAuthorAsync(
+        string authorId,
+        CancellationToken cancellationToken)
+    {
+        var (authorTable, authorIdPart) = SurrealRecordId.Split(authorId);
+
+        var response = await _client.RawQuery(
+            $"SELECT {SelectIdeaFields} FROM idea WHERE author = type::record($authorTable, $authorId) " +
+            "ORDER BY updated_at DESC;",
+            new Dictionary<string, object?>
+            {
+                ["authorTable"] = authorTable,
+                ["authorId"] = authorIdPart,
+            },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<IdeaRow>>(0) ?? [];
+        var result = new List<IdeaResponse>(rows.Count);
+
+        foreach (var row in rows)
+        {
+            result.Add(Map(row, await LoadCardAsync(row.Id, cancellationToken)));
+        }
+
+        return result;
+    }
+
+    public async Task<IdeaResponse?> UpdateAsync(
+        string ideaId,
+        UpdateIdeaRequest request,
+        CancellationToken cancellationToken)
+    {
+        var (table, id) = SurrealRecordId.Split(ideaId);
+        var parameters = new Dictionary<string, object?>
+        {
+            ["table"] = table,
+            ["id"] = id,
+            ["title"] = request.Title,
+            ["description"] = request.Description,
+        };
+
+        var assignments = new List<string>
+        {
+            "title = $title", "description = $description", "updated_at = time::now()",
+        };
+
+        if (!string.IsNullOrWhiteSpace(request.Status) && IdeaStatusWire.Parse(request.Status) is { } status)
+        {
+            assignments.Add("status = $status");
+            parameters["status"] = status.ToWire();
+        }
+
+        var response = await _client.RawQuery(
+            $"UPDATE type::record($table, $id) SET {string.Join(", ", assignments)}; " +
+            $"SELECT {SelectIdeaFields} FROM type::record($table, $id) LIMIT 1;",
+            parameters,
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<IdeaRow>>(1) ?? [];
+
+        if (rows.Count == 0)
+        {
+            return null;
+        }
+
+        return Map(rows[0], await LoadCardAsync(ideaId, cancellationToken));
+    }
+
+    public async Task<IdeaCardResponse?> GetCardAsync(string ideaId, CancellationToken cancellationToken) =>
+        await LoadCardAsync(ideaId, cancellationToken);
+
+    public async Task<IdeaCardResponse?> UpdateCardAsync(
+        string ideaId,
+        IdeaCardRequest request,
+        CancellationToken cancellationToken)
+    {
+        var (table, id) = SurrealRecordId.Split(ideaId);
+
+        var response = await _client.RawQuery(
+            "UPDATE idea_card SET essence = $essence, audience = $audience, stage = $stage " +
+            "WHERE idea = type::record($table, $id); " +
+            $"SELECT {SelectCardFields} FROM idea_card WHERE idea = type::record($table, $id) LIMIT 1;",
+            new Dictionary<string, object?>
+            {
+                ["table"] = table,
+                ["id"] = id,
+                ["essence"] = request.Essence ?? string.Empty,
+                ["audience"] = request.Audience ?? string.Empty,
+                ["stage"] = string.IsNullOrWhiteSpace(request.Stage) ? "idea" : request.Stage,
+            },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<IdeaCardRow>>(1) ?? [];
+
+        return rows.Count > 0 ? MapCard(rows[0]) : null;
+    }
+
+    private async Task<IdeaResponse?> LoadAsync(string ideaId, CancellationToken cancellationToken)
+    {
+        var (table, id) = SurrealRecordId.Split(ideaId);
+
+        var response = await _client.RawQuery(
+            $"SELECT {SelectIdeaFields} FROM type::record($table, $id) LIMIT 1;",
+            new Dictionary<string, object?> { ["table"] = table, ["id"] = id },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<IdeaRow>>(0) ?? [];
+
+        if (rows.Count == 0)
+        {
+            return null;
+        }
+
+        return Map(rows[0], await LoadCardAsync(ideaId, cancellationToken));
+    }
+
+    private async Task<IdeaCardResponse?> LoadCardAsync(string ideaId, CancellationToken cancellationToken)
+    {
+        var (table, id) = SurrealRecordId.Split(ideaId);
+
+        var response = await _client.RawQuery(
+            $"SELECT {SelectCardFields} FROM idea_card WHERE idea = type::record($table, $id) LIMIT 1;",
+            new Dictionary<string, object?> { ["table"] = table, ["id"] = id },
+            cancellationToken);
+        response.EnsureAllOks();
+
+        var rows = response.GetValue<List<IdeaCardRow>>(0) ?? [];
+
+        return rows.Count > 0 ? MapCard(rows[0]) : null;
+    }
+
+    private static IdeaResponse Map(IdeaRow row, IdeaCardResponse? card) => new(
+        row.Id,
+        row.Title,
+        row.Description,
+        row.Author,
+        row.Status,
+        card,
+        row.UpdatedAt);
+
+    private static IdeaCardResponse MapCard(IdeaCardRow row) => new(
+        row.Id,
+        row.Idea,
+        row.Essence,
+        row.Audience,
+        row.Stage);
+}
diff --git a/backend/Infrastructure/Persistence/SurrealRows.cs b/backend/Infrastructure/Persistence/SurrealRows.cs
index a8f975b..cc20393 100644
--- a/backend/Infrastructure/Persistence/SurrealRows.cs
+++ b/backend/Infrastructure/Persistence/SurrealRows.cs
@@ -155,3 +155,61 @@ internal sealed class IdRow
 {
     [CborProperty("id")] public string Id { get; set; } = string.Empty;
 }
+
+internal sealed class IdeaRow
+{
+    [CborProperty("id")] public string Id { get; set; } = string.Empty;
+
+    [CborProperty("title")] public string Title { get; set; } = string.Empty;
+
+    [CborProperty("description")] public string Description { get; set; } = string.Empty;
+
+    [CborProperty("author")] public string Author { get; set; } = string.Empty;
+
+    [CborProperty("status")] public string Status { get; set; } = string.Empty;
+
+    [CborProperty("updated_at")] public DateTimeOffset? UpdatedAt { get; set; }
+}
+
+internal sealed class IdeaCardRow
+{
+    [CborProperty("id")] public string Id { get; set; } = string.Empty;
+
+    [CborProperty("idea")] public string Idea { get; set; } = string.Empty;
+
+    [CborProperty("essence")] public string Essence { get; set; } = string.Empty;
+
+    [CborProperty("audience")] public string Audience { get; set; } = string.Empty;
+
+    [CborProperty("stage")] public string Stage { get; set; } = string.Empty;
+}
+
+internal sealed class GrantCallRow
+{
+    [CborProperty("id")] public string Id { get; set; } = string.Empty;
+
+    [CborProperty("name")] public string Name { get; set; } = string.Empty;
+
+    [CborProperty("opens_at")] public DateTimeOffset OpensAt { get; set; }
+
+    [CborProperty("closes_at")] public DateTimeOffset ClosesAt { get; set; }
+
+    [CborProperty("status")] public string Status { get; set; } = string.Empty;
+
+    [CborProperty("external_id")] public string? ExternalId { get; set; }
+}
+
+internal sealed class ApplicationRow
+{
+    [CborProperty("id")] public string Id { get; set; } = string.Empty;
+
+    [CborProperty("grant_call")] public string GrantCall { get; set; } = string.Empty;
+
+    [CborProperty("idea")] public string Idea { get; set; } = string.Empty;
+
+    [CborProperty("content")] public Dictionary<string, string?> Content { get; set; } = [];
+
+    [CborProperty("status")] public string Status { get; set; } = string.Empty;
+
+    [CborProperty("created_at")] public DateTimeOffset CreatedAt { get; set; }
+}