diff --git a/Webshop.Api/Controllers/Admin/AdminSuppliersController.cs b/Webshop.Api/Controllers/Admin/AdminSuppliersController.cs
index c949d7a..61a295b 100644
--- a/Webshop.Api/Controllers/Admin/AdminSuppliersController.cs
+++ b/Webshop.Api/Controllers/Admin/AdminSuppliersController.cs
@@ -1,9 +1,11 @@
 // src/Webshop.Api/Controllers/Admin/AdminSuppliersController.cs
 using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using Webshop.Application;
 using Webshop.Application.DTOs.Suppliers;
 using Webshop.Application.Services.Admin.Interfaces;
 
@@ -14,7 +16,6 @@ namespace Webshop.Api.Controllers.Admin
     [Authorize(Roles = "Admin")]
     public class AdminSuppliersController : ControllerBase
     {
-        // Der Controller hängt vom Interface ab, nicht von der konkreten Klasse
         private readonly IAdminSupplierService _adminSupplierService;
 
         public AdminSuppliersController(IAdminSupplierService adminSupplierService)
@@ -23,49 +24,89 @@ namespace Webshop.Api.Controllers.Admin
         }
 
         [HttpGet]
-        public async Task<ActionResult<IEnumerable<SupplierDto>>> GetAllSuppliers()
+        [ProducesResponseType(typeof(IEnumerable<SupplierDto>), StatusCodes.Status200OK)]
+        public async Task<IActionResult> GetAllSuppliers()
         {
-            var suppliers = await _adminSupplierService.GetAllSuppliersAsync();
-            return Ok(suppliers);
+            var result = await _adminSupplierService.GetAllSuppliersAsync();
+            return Ok(result.Value);
         }
 
         [HttpGet("{id:guid}")]
-        public async Task<ActionResult<SupplierDto>> GetSupplierById(Guid id)
+        [ProducesResponseType(typeof(SupplierDto), StatusCodes.Status200OK)]
+        [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound)]
+        public async Task<IActionResult> GetSupplierById(Guid id)
         {
-            var supplier = await _adminSupplierService.GetSupplierByIdAsync(id);
-            if (supplier == null) return NotFound();
-            return Ok(supplier);
+            var result = await _adminSupplierService.GetSupplierByIdAsync(id);
+
+            return result.Type switch
+            {
+                ServiceResultType.Success => Ok(result.Value),
+                ServiceResultType.NotFound => NotFound(new { Message = result.ErrorMessage }),
+                _ => StatusCode(StatusCodes.Status500InternalServerError, new { Message = result.ErrorMessage ?? "Ein unerwarteter Fehler ist aufgetreten." })
+            };
         }
 
         [HttpPost]
-        public async Task<ActionResult<SupplierDto>> CreateSupplier([FromBody] SupplierDto supplierDto)
+        [ProducesResponseType(typeof(SupplierDto), StatusCodes.Status201Created)]
+        [ProducesResponseType(typeof(ValidationProblemDetails), StatusCodes.Status400BadRequest)]
+        [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status409Conflict)]
+        public async Task<IActionResult> CreateSupplier([FromBody] SupplierDto supplierDto)
         {
-            if (supplierDto == null) return BadRequest("Supplier data is required.");
-            if (!ModelState.IsValid) return BadRequest(ModelState);
+            if (!ModelState.IsValid)
+            {
+                return BadRequest(ModelState);
+            }
 
-            var createdSupplier = await _adminSupplierService.CreateSupplierAsync(supplierDto);
-            return CreatedAtAction(nameof(GetSupplierById), new { id = createdSupplier.Id }, createdSupplier);
+            var result = await _adminSupplierService.CreateSupplierAsync(supplierDto);
+
+            return result.Type switch
+            {
+                ServiceResultType.Success => CreatedAtAction(nameof(GetSupplierById), new { id = result.Value!.Id }, result.Value),
+                ServiceResultType.Conflict => Conflict(new { Message = result.ErrorMessage }),
+                _ => StatusCode(StatusCodes.Status500InternalServerError, new { Message = result.ErrorMessage ?? "Ein unerwarteter Fehler ist aufgetreten." })
+            };
         }
 
         [HttpPut("{id:guid}")]
+        [ProducesResponseType(StatusCodes.Status204NoContent)]
+        [ProducesResponseType(typeof(ValidationProblemDetails), StatusCodes.Status400BadRequest)]
+        [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound)]
+        [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status409Conflict)]
         public async Task<IActionResult> UpdateSupplier(Guid id, [FromBody] SupplierDto supplierDto)
         {
-            if (id != supplierDto.Id) return BadRequest("Mismatched ID in route and body.");
-            if (!ModelState.IsValid) return BadRequest(ModelState);
+            if (id != supplierDto.Id)
+            {
+                return BadRequest(new { Message = "ID in der URL und im Body stimmen nicht überein." });
+            }
+            if (!ModelState.IsValid)
+            {
+                return BadRequest(ModelState);
+            }
 
-            var success = await _adminSupplierService.UpdateSupplierAsync(id, supplierDto);
-            if (!success) return NotFound();
+            var result = await _adminSupplierService.UpdateSupplierAsync(supplierDto);
 
-            return NoContent(); // Standardantwort für erfolgreiches Update
+            return result.Type switch
+            {
+                ServiceResultType.Success => NoContent(),
+                ServiceResultType.NotFound => NotFound(new { Message = result.ErrorMessage }),
+                ServiceResultType.Conflict => Conflict(new { Message = result.ErrorMessage }),
+                _ => StatusCode(StatusCodes.Status500InternalServerError, new { Message = result.ErrorMessage ?? "Ein unerwarteter Fehler ist aufgetreten." })
+            };
         }
 
         [HttpDelete("{id:guid}")]
+        [ProducesResponseType(StatusCodes.Status204NoContent)]
+        [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound)]
         public async Task<IActionResult> DeleteSupplier(Guid id)
         {
-            var success = await _adminSupplierService.DeleteSupplierAsync(id);
-            if (!success) return NotFound();
+            var result = await _adminSupplierService.DeleteSupplierAsync(id);
 
-            return NoContent(); // Standardantwort für erfolgreiches Löschen
+            return result.Type switch
+            {
+                ServiceResultType.Success => NoContent(),
+                ServiceResultType.NotFound => NotFound(new { Message = result.ErrorMessage }),
+                _ => StatusCode(StatusCodes.Status500InternalServerError, new { Message = result.ErrorMessage ?? "Ein unerwarteter Fehler ist aufgetreten." })
+            };
         }
     }
 }
\ No newline at end of file
diff --git a/Webshop.Application/Services/Admin/AdminSupplierService.cs b/Webshop.Application/Services/Admin/AdminSupplierService.cs
index b11777d..69cae8e 100644
--- a/Webshop.Application/Services/Admin/AdminSupplierService.cs
+++ b/Webshop.Application/Services/Admin/AdminSupplierService.cs
@@ -1,64 +1,50 @@
 // src/Webshop.Application/Services/Admin/AdminSupplierService.cs
 using Webshop.Domain.Entities;
-using Webshop.Domain.Interfaces; // Wichtig für ISupplierRepository
+using Webshop.Domain.Interfaces;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
+using Webshop.Application;
 using Webshop.Application.DTOs.Suppliers;
 using Webshop.Application.Services.Admin.Interfaces;
-using Webshop.Domain.Identity;
 
 namespace Webshop.Application.Services.Admin
 {
-    // Implementiert das Interface, das der Controller erwartet
     public class AdminSupplierService : IAdminSupplierService
     {
         private readonly ISupplierRepository _supplierRepository;
 
-        // Lässt sich das Repository per Dependency Injection geben
         public AdminSupplierService(ISupplierRepository supplierRepository)
         {
             _supplierRepository = supplierRepository;
         }
 
-        public async Task<IEnumerable<SupplierDto>> GetAllSuppliersAsync()
+        public async Task<ServiceResult<IEnumerable<SupplierDto>>> GetAllSuppliersAsync()
         {
             var suppliers = await _supplierRepository.GetAllSuppliersAsync();
-            // Mappt die Entity-Liste zu einer DTO-Liste für die API
-            return suppliers.Select(s => new SupplierDto
-            {
-                Id = s.Id,
-                Name = s.Name,
-                ContactPerson = s.ContactPerson,
-                Email = s.Email,
-                PhoneNumber = s.PhoneNumber,
-                AddressId = s.AddressId,
-                Notes = s.Notes
-            });
+            var dtos = suppliers.Select(MapToDto);
+            return ServiceResult.Ok<IEnumerable<SupplierDto>>(dtos);
         }
 
-        public async Task<SupplierDto?> GetSupplierByIdAsync(Guid id)
+        public async Task<ServiceResult<SupplierDto>> GetSupplierByIdAsync(Guid id)
         {
             var supplier = await _supplierRepository.GetSupplierByIdAsync(id);
-            if (supplier == null) return null;
-
-            // Mappt die gefundene Entity zu einem DTO
-            return new SupplierDto
+            if (supplier == null)
             {
-                Id = supplier.Id,
-                Name = supplier.Name,
-                ContactPerson = supplier.ContactPerson,
-                Email = supplier.Email,
-                PhoneNumber = supplier.PhoneNumber,
-                AddressId = supplier.AddressId,
-                Notes = supplier.Notes
-            };
+                return ServiceResult.Fail<SupplierDto>(ServiceResultType.NotFound, $"Lieferant mit ID '{id}' nicht gefunden.");
+            }
+            return ServiceResult.Ok(MapToDto(supplier));
         }
 
-        public async Task<SupplierDto> CreateSupplierAsync(SupplierDto supplierDto)
+        public async Task<ServiceResult<SupplierDto>> CreateSupplierAsync(SupplierDto supplierDto)
         {
-            // Wandelt das DTO von der API in eine Datenbank-Entity um
+            var allSuppliers = await _supplierRepository.GetAllSuppliersAsync();
+            if (allSuppliers.Any(s => s.Name.Equals(supplierDto.Name, StringComparison.OrdinalIgnoreCase)))
+            {
+                return ServiceResult.Fail<SupplierDto>(ServiceResultType.Conflict, $"Ein Lieferant mit dem Namen '{supplierDto.Name}' existiert bereits.");
+            }
+
             var supplier = new Supplier
             {
                 Name = supplierDto.Name,
@@ -71,20 +57,24 @@ namespace Webshop.Application.Services.Admin
 
             await _supplierRepository.AddSupplierAsync(supplier);
 
-            // Gibt ein DTO mit der neu generierten ID zurück
             supplierDto.Id = supplier.Id;
-            return supplierDto;
+            return ServiceResult.Ok(supplierDto);
         }
 
-        public async Task<bool> UpdateSupplierAsync(Guid id, SupplierDto supplierDto)
+        public async Task<ServiceResult> UpdateSupplierAsync(SupplierDto supplierDto)
         {
-            var existingSupplier = await _supplierRepository.GetSupplierByIdAsync(id);
+            var existingSupplier = await _supplierRepository.GetSupplierByIdAsync(supplierDto.Id);
             if (existingSupplier == null)
             {
-                return false; // Konnte nicht gefunden werden
+                return ServiceResult.Fail(ServiceResultType.NotFound, $"Lieferant mit ID '{supplierDto.Id}' nicht gefunden.");
+            }
+
+            var allSuppliers = await _supplierRepository.GetAllSuppliersAsync();
+            if (allSuppliers.Any(s => s.Name.Equals(supplierDto.Name, StringComparison.OrdinalIgnoreCase) && s.Id != supplierDto.Id))
+            {
+                return ServiceResult.Fail(ServiceResultType.Conflict, $"Ein anderer Lieferant mit dem Namen '{supplierDto.Name}' existiert bereits.");
             }
 
-            // Aktualisiert die Daten der gefundenen Entity
             existingSupplier.Name = supplierDto.Name;
             existingSupplier.ContactPerson = supplierDto.ContactPerson;
             existingSupplier.Email = supplierDto.Email;
@@ -93,19 +83,39 @@ namespace Webshop.Application.Services.Admin
             existingSupplier.Notes = supplierDto.Notes;
 
             await _supplierRepository.UpdateSupplierAsync(existingSupplier);
-            return true;
+            return ServiceResult.Ok();
         }
 
-        public async Task<bool> DeleteSupplierAsync(Guid id)
+        public async Task<ServiceResult> DeleteSupplierAsync(Guid id)
         {
             var supplier = await _supplierRepository.GetSupplierByIdAsync(id);
             if (supplier == null)
             {
-                return false; // Konnte nicht gefunden werden
+                return ServiceResult.Fail(ServiceResultType.NotFound, $"Lieferant mit ID '{id}' nicht gefunden.");
             }
 
+            // Hier könnte man noch prüfen, ob der Lieferant Produkten zugeordnet ist (Conflict)
+            // if (await _productRepository.AnyAsync(p => p.SupplierId == id))
+            // {
+            //     return ServiceResult.Fail(ServiceResultType.Conflict, "Lieferant kann nicht gelöscht werden, da ihm Produkte zugeordnet sind.");
+            // }
+
             await _supplierRepository.DeleteSupplierAsync(id);
-            return true;
+            return ServiceResult.Ok();
+        }
+
+        private SupplierDto MapToDto(Supplier s)
+        {
+            return new SupplierDto
+            {
+                Id = s.Id,
+                Name = s.Name,
+                ContactPerson = s.ContactPerson,
+                Email = s.Email,
+                PhoneNumber = s.PhoneNumber,
+                AddressId = s.AddressId,
+                Notes = s.Notes
+            };
         }
     }
 }
\ No newline at end of file
diff --git a/Webshop.Application/Services/Admin/Interfaces/IAdminSupplierService.cs b/Webshop.Application/Services/Admin/Interfaces/IAdminSupplierService.cs
index bf6d643..3844528 100644
--- a/Webshop.Application/Services/Admin/Interfaces/IAdminSupplierService.cs
+++ b/Webshop.Application/Services/Admin/Interfaces/IAdminSupplierService.cs
@@ -1,21 +1,18 @@
 // src/Webshop.Application/Services/Admin/IAdminSupplierService.cs
-
-using System; // Für Guid
+using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using Webshop.Application;
 using Webshop.Application.DTOs.Suppliers;
 
 namespace Webshop.Application.Services.Admin.Interfaces
 {
     public interface IAdminSupplierService
     {
-        // Diese Methoden waren bereits vorhanden
-        Task<IEnumerable<SupplierDto>> GetAllSuppliersAsync();
-        Task<SupplierDto?> GetSupplierByIdAsync(Guid id);
-        Task<SupplierDto> CreateSupplierAsync(SupplierDto supplierDto);
-
-        // --- HIER DIE FEHLENDEN METHODEN ERGÄNZEN ---
-        Task<bool> UpdateSupplierAsync(Guid id, SupplierDto supplierDto);
-        Task<bool> DeleteSupplierAsync(Guid id);
+        Task<ServiceResult<IEnumerable<SupplierDto>>> GetAllSuppliersAsync();
+        Task<ServiceResult<SupplierDto>> GetSupplierByIdAsync(Guid id);
+        Task<ServiceResult<SupplierDto>> CreateSupplierAsync(SupplierDto supplierDto);
+        Task<ServiceResult> UpdateSupplierAsync(SupplierDto supplierDto); // Parameter vereinfacht
+        Task<ServiceResult> DeleteSupplierAsync(Guid id);
     }
 }
\ No newline at end of file