diff --git a/Distribution/Features/PurchaseOrder/IPoRepository.cs b/Distribution/Features/PurchaseOrder/IPoRepository.cs
new file mode 100644
index 0000000..9844faf
--- /dev/null
+++ b/Distribution/Features/PurchaseOrder/IPoRepository.cs
@@ -0,0 +1,19 @@
+using Distribution.Models;
+
+namespace Distribution.Features.Po;
+
+public interface IPoRepository
+{
+    Task<Models.PurchaseOrder?> GetByIdAsync(Guid id);
+    Task<List<Models.PurchaseOrder>> GetAllAsync(Guid? supplierId, PurchaseOrderStatus? status);
+    Task AddAsync(Models.PurchaseOrder entity);
+    void Update(Models.PurchaseOrder entity);
+
+    Task AddItemAsync(PurchaseOrderItem entity);
+
+    /// <summary>True if any active (non-cancelled, non-closed-and-void) PurchaseOrder references this supplier.</summary>
+    Task<bool> HasActiveForSupplierAsync(Guid supplierId);
+
+    /// <summary>All active PurchaseOrders for a supplier, with items, used by evaluateSupplier.</summary>
+    Task<List<Models.PurchaseOrder>> GetBySupplierAsync(Guid supplierId);
+}
diff --git a/Distribution/Features/PurchaseOrder/PoController.cs b/Distribution/Features/PurchaseOrder/PoController.cs
new file mode 100644
index 0000000..c1fa3dc
--- /dev/null
+++ b/Distribution/Features/PurchaseOrder/PoController.cs
@@ -0,0 +1,97 @@
+using Distribution.Infra.Authorization;
+using Distribution.Models;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Distribution.Features.Po;
+
+[ApiController]
+[Route("api/purchase-orders")]
+[Authorize]
+public class PoController(PoService service, ICurrentUserService currentUser) : ControllerBase
+{
+    [HttpGet]
+    public async Task<IActionResult> GetAll([FromQuery] Guid? supplierId, [FromQuery] PurchaseOrderStatus? status) =>
+        Ok(await service.GetAllAsync(supplierId, status));
+
+    [HttpGet("{id:guid}")]
+    public async Task<IActionResult> GetById(Guid id)
+    {
+        var result = await service.GetByIdAsync(id);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpPost]
+    public async Task<IActionResult> Create(CreatePoRequest request, CancellationToken ct)
+    {
+        var userId = currentUser.UserId ?? throw new UnauthorizedAccessException();
+        try
+        {
+            var result = await service.CreateAsync(request, userId, ct);
+            return CreatedAtAction(nameof(GetById), new { id = result.Id }, result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPut("{id:guid}")]
+    public async Task<IActionResult> Update(Guid id, UpdatePoRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.UpdateAsync(id, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/close")]
+    public async Task<IActionResult> Close(Guid id, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.CloseAsync(id, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/cancel")]
+    public async Task<IActionResult> Cancel(Guid id, CancelPoRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.CancelAsync(id, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/items/{itemId:guid}/cancel")]
+    public async Task<IActionResult> CancelLine(Guid id, Guid itemId, CancelPoLineRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.CancelLineAsync(id, itemId, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+
+    [HttpPost("{id:guid}/match-invoice")]
+    public async Task<IActionResult> MatchInvoice(Guid id, [FromQuery] Guid? invoiceId, [FromQuery] Guid? grnId)
+    {
+        var result = await service.MatchInvoiceToPoAsync(id, invoiceId, grnId);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpPost("{id:guid}/resolve-variance")]
+    public async Task<IActionResult> ResolveVariance(Guid id, ResolveInvoiceVarianceRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.ResolveInvoiceVarianceAsync(id, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return Conflict(new { error = ex.Message }); }
+    }
+}
diff --git a/Distribution/Features/PurchaseOrder/PoDTOs.cs b/Distribution/Features/PurchaseOrder/PoDTOs.cs
new file mode 100644
index 0000000..7c9868b
--- /dev/null
+++ b/Distribution/Features/PurchaseOrder/PoDTOs.cs
@@ -0,0 +1,54 @@
+using Distribution.Models;
+
+namespace Distribution.Features.Po;
+
+public record PoItemRequest(Guid ItemId, int Quantity, decimal UnitCost);
+
+public record CreatePoRequest(Guid SupplierId, List<PoItemRequest> Items);
+
+/// <summary>
+/// Update line: PurchaseOrderItemId set = update an existing unreceived line (Quantity/UnitCost),
+/// null = add a new line to the Po. Only valid while the Po is Issued.
+/// </summary>
+public record UpdatePoLineRequest(Guid? PurchaseOrderItemId, Guid ItemId, int Quantity, decimal UnitCost);
+
+public record UpdatePoRequest(List<UpdatePoLineRequest> Items);
+
+public record CancelPoRequest(string Reason);
+
+public record CancelPoLineRequest(string? Reason);
+
+public record PoItemResponse(
+    Guid Id,
+    Guid ItemId,
+    string Sku,
+    string ItemName,
+    int Quantity,
+    decimal UnitCost,
+    int ReceivedQuantity,
+    int CancelledQuantity,
+    bool IsCancelled);
+
+public record PoResponse(
+    Guid Id,
+    Guid SupplierId,
+    string SupplierName,
+    Guid CreatedByUserId,
+    PurchaseOrderStatus Status,
+    string? CancelReason,
+    bool IsActive,
+    DateTime CreatedAt,
+    List<PoItemResponse> Items);
+
+/// <summary>
+/// Minimal Po-vs-Grn quantity/cost reconciliation. Full 3-way match (Po + Grn + Invoice) activates
+/// once Finance's Invoice entity (step 19, not yet built) exists — until then this compares only
+/// PurchaseOrderItem vs GoodsReceiptItem.
+/// </summary>
+public record InvoiceMatchLineResult(Guid PurchaseOrderItemId, Guid ItemId, int OrderedQuantity, int AcceptedQuantity, decimal UnitCost, bool QuantityMatches);
+
+public record InvoiceMatchResult(Guid PurchaseOrderId, Guid? GoodsReceiptId, Guid? InvoiceId, bool IsMatched, List<InvoiceMatchLineResult> Lines, string Note);
+
+public record ResolveInvoiceVarianceRequest(string Variance, string Resolution, decimal? AdjustedUnitCost, Guid? PurchaseOrderItemId);
+
+public record InvoiceVarianceResolutionResponse(Guid PurchaseOrderId, string Variance, string Resolution, DateTime ResolvedAt);
diff --git a/Distribution/Features/PurchaseOrder/PoRepository.cs b/Distribution/Features/PurchaseOrder/PoRepository.cs
new file mode 100644
index 0000000..334dc6e
--- /dev/null
+++ b/Distribution/Features/PurchaseOrder/PoRepository.cs
@@ -0,0 +1,49 @@
+using Distribution.Data;
+using Distribution.Models;
+using Microsoft.EntityFrameworkCore;
+
+namespace Distribution.Features.Po;
+
+public class PoRepository(AppDBContext context) : IPoRepository
+{
+    public async Task<Models.PurchaseOrder?> GetByIdAsync(Guid id) =>
+        await context.PurchaseOrders
+            .Include(po => po.Supplier)
+            .Include(po => po.Items).ThenInclude(i => i.Item)
+            .FirstOrDefaultAsync(po => po.Id == id);
+
+    public async Task<List<Models.PurchaseOrder>> GetAllAsync(Guid? supplierId, PurchaseOrderStatus? status)
+    {
+        var query = context.PurchaseOrders
+            .Include(po => po.Supplier)
+            .Include(po => po.Items).ThenInclude(i => i.Item)
+            .Where(po => po.IsActive)
+            .AsQueryable();
+
+        if (supplierId.HasValue) query = query.Where(po => po.FK_SupplierId == supplierId.Value);
+        if (status.HasValue) query = query.Where(po => po.Status == status.Value);
+
+        return await query.OrderByDescending(po => po.CreatedAt).ToListAsync();
+    }
+
+    public async Task AddAsync(Models.PurchaseOrder entity) =>
+        await context.PurchaseOrders.AddAsync(entity);
+
+    public void Update(Models.PurchaseOrder entity) =>
+        context.PurchaseOrders.Update(entity);
+
+    public async Task AddItemAsync(PurchaseOrderItem entity) =>
+        await context.PurchaseOrderItems.AddAsync(entity);
+
+    public async Task<bool> HasActiveForSupplierAsync(Guid supplierId) =>
+        await context.PurchaseOrders.AnyAsync(po =>
+            po.FK_SupplierId == supplierId &&
+            po.IsActive &&
+            po.Status != PurchaseOrderStatus.Cancelled);
+
+    public async Task<List<Models.PurchaseOrder>> GetBySupplierAsync(Guid supplierId) =>
+        await context.PurchaseOrders
+            .Include(po => po.Items)
+            .Where(po => po.FK_SupplierId == supplierId && po.IsActive)
+            .ToListAsync();
+}
diff --git a/Distribution/Features/PurchaseOrder/PoService.cs b/Distribution/Features/PurchaseOrder/PoService.cs
new file mode 100644
index 0000000..11184d0
--- /dev/null
+++ b/Distribution/Features/PurchaseOrder/PoService.cs
@@ -0,0 +1,245 @@
+using Distribution.Features.Grn;
+using Distribution.Infra.UoW;
+using Distribution.Models;
+
+namespace Distribution.Features.Po;
+
+public class PoService(
+    IPoRepository repo,
+    IGrnRepository goodsReceiptRepo,
+    IUnitOfWork uow)
+{
+    private static PoItemResponse MapItem(PurchaseOrderItem i) =>
+        new(i.Id, i.FK_ItemId, i.Item.Sku, i.Item.Name, i.Quantity, i.UnitCost, i.ReceivedQuantity, i.CancelledQuantity, i.IsCancelled);
+
+    private static PoResponse Map(Models.PurchaseOrder po) =>
+        new(po.Id, po.FK_SupplierId, po.Supplier?.Name ?? string.Empty, po.FK_CreatedByUserId,
+            po.Status, po.CancelReason, po.IsActive, po.CreatedAt,
+            po.Items.Where(i => i.IsActive).Select(MapItem).ToList());
+
+    public async Task<List<PoResponse>> GetAllAsync(Guid? supplierId, PurchaseOrderStatus? status) =>
+        (await repo.GetAllAsync(supplierId, status)).Select(Map).ToList();
+
+    public async Task<PoResponse?> GetByIdAsync(Guid id)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+        return Map(po);
+    }
+
+    public async Task<PoResponse> CreateAsync(CreatePoRequest request, Guid createdByUserId, CancellationToken ct = default)
+    {
+        if (request.Items is null || request.Items.Count == 0)
+            throw new InvalidOperationException("A purchase order must have at least one line item.");
+
+        var po = new Models.PurchaseOrder
+        {
+            FK_SupplierId = request.SupplierId,
+            FK_CreatedByUserId = createdByUserId,
+            Status = PurchaseOrderStatus.Issued
+        };
+
+        foreach (var line in request.Items)
+        {
+            po.Items.Add(new PurchaseOrderItem
+            {
+                FK_ItemId = line.ItemId,
+                Quantity = line.Quantity,
+                UnitCost = line.UnitCost
+            });
+        }
+
+        await uow.BeginAsync(ct);
+        try { await repo.AddAsync(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return (await GetByIdAsync(po.Id))!;
+    }
+
+    /// <summary>
+    /// May only change unreceived lines (ReceivedQuantity == 0) and only while the Po is Issued.
+    /// Lines with a PurchaseOrderItemId update an existing line; lines without one add a new line.
+    /// </summary>
+    public async Task<PoResponse?> UpdateAsync(Guid id, UpdatePoRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        if (po.Status != PurchaseOrderStatus.Issued)
+            throw new InvalidOperationException($"Cannot update a purchase order in {po.Status} status; only an Issued Po can be updated.");
+
+        await uow.BeginAsync(ct);
+        try
+        {
+            foreach (var line in request.Items)
+            {
+                if (line.PurchaseOrderItemId.HasValue)
+                {
+                    var existing = po.Items.FirstOrDefault(i => i.Id == line.PurchaseOrderItemId.Value && i.IsActive)
+                        ?? throw new InvalidOperationException($"Purchase order line {line.PurchaseOrderItemId} not found on this Po.");
+
+                    if (existing.ReceivedQuantity > 0)
+                        throw new InvalidOperationException(
+                            $"Line for item {existing.FK_ItemId} has already received stock and cannot be edited; use cancelPurchaseOrderLine or createPurchaseReturn instead.");
+
+                    existing.FK_ItemId = line.ItemId;
+                    existing.Quantity = line.Quantity;
+                    existing.UnitCost = line.UnitCost;
+                }
+                else
+                {
+                    await repo.AddItemAsync(new PurchaseOrderItem
+                    {
+                        FK_PurchaseOrderId = po.Id,
+                        FK_ItemId = line.ItemId,
+                        Quantity = line.Quantity,
+                        UnitCost = line.UnitCost
+                    });
+                }
+            }
+
+            repo.Update(po);
+            await uow.CommitAsync(ct);
+        }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return (await GetByIdAsync(id))!;
+    }
+
+    /// <summary>
+    /// Only valid once a Po is Received, or manually closed early (outstanding quantity written off).
+    /// </summary>
+    public async Task<PoResponse?> CloseAsync(Guid id, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        if (po.Status is PurchaseOrderStatus.Closed or PurchaseOrderStatus.Cancelled)
+            throw new InvalidOperationException($"Cannot close a purchase order already in {po.Status} status.");
+
+        po.Status = PurchaseOrderStatus.Closed;
+
+        await uow.BeginAsync(ct);
+        try { repo.Update(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return Map(po);
+    }
+
+    /// <summary>Only valid before any goods receipt exists against the Po.</summary>
+    public async Task<PoResponse?> CancelAsync(Guid id, CancelPoRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        if (po.Status is PurchaseOrderStatus.Closed or PurchaseOrderStatus.Cancelled)
+            throw new InvalidOperationException($"Cannot cancel a purchase order already in {po.Status} status.");
+
+        if (await goodsReceiptRepo.HasAnyForPurchaseOrderAsync(id))
+            throw new InvalidOperationException("Cannot cancel a purchase order that already has a goods receipt against it.");
+
+        po.Status = PurchaseOrderStatus.Cancelled;
+        po.CancelReason = request.Reason;
+
+        await uow.BeginAsync(ct);
+        try { repo.Update(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return Map(po);
+    }
+
+    /// <summary>
+    /// Cancels a single line instead of the whole Po. Only valid while ReceivedQuantity &lt; Quantity
+    /// and the line isn't already fully received or cancelled. Auto-completes the Po to Received once
+    /// every non-cancelled line is fully received.
+    /// </summary>
+    public async Task<PoResponse?> CancelLineAsync(Guid id, Guid poItemId, CancelPoLineRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(id);
+        if (po is null || !po.IsActive) return null;
+
+        var line = po.Items.FirstOrDefault(i => i.Id == poItemId && i.IsActive)
+            ?? throw new InvalidOperationException("Purchase order line not found on this Po.");
+
+        if (line.IsCancelled)
+            throw new InvalidOperationException("This line is already cancelled.");
+
+        if (line.ReceivedQuantity >= line.Quantity)
+            throw new InvalidOperationException("This line is already fully received and cannot be cancelled.");
+
+        line.IsCancelled = true;
+        line.CancelledQuantity = line.Quantity - line.ReceivedQuantity;
+
+        var activeLines = po.Items.Where(i => i.IsActive).ToList();
+        if (activeLines.Where(i => !i.IsCancelled).All(i => i.ReceivedQuantity >= i.Quantity)
+            && activeLines.Any(i => !i.IsCancelled))
+        {
+            po.Status = PurchaseOrderStatus.Received;
+        }
+
+        await uow.BeginAsync(ct);
+        try { repo.Update(po); await uow.CommitAsync(ct); }
+        catch { await uow.RollbackAsync(ct); throw; }
+
+        return Map(po);
+    }
+
+    /// <summary>
+    /// Minimal Po-vs-Grn reconciliation (matchInvoiceToPo). Full 3-way match against an Invoice
+    /// entity activates once Finance (step 19) exists; this only detects and reports, never adjusts.
+    /// </summary>
+    public async Task<InvoiceMatchResult?> MatchInvoiceToPoAsync(Guid poId, Guid? invoiceId, Guid? grnId)
+    {
+        var po = await repo.GetByIdAsync(poId);
+        if (po is null || !po.IsActive) return null;
+
+        var receipts = grnId.HasValue
+            ? (await goodsReceiptRepo.GetByPurchaseOrderIdAsync(poId)).Where(g => g.Id == grnId.Value).ToList()
+            : await goodsReceiptRepo.GetByPurchaseOrderIdAsync(poId);
+
+        var acceptedByItem = receipts
+            .SelectMany(g => g.Items.Where(i => i.IsActive))
+            .GroupBy(i => i.PurchaseOrderItem.FK_ItemId)
+            .ToDictionary(g => g.Key, g => g.Sum(i => i.AcceptedQuantity));
+
+        var lines = po.Items.Where(i => i.IsActive).Select(i =>
+        {
+            acceptedByItem.TryGetValue(i.FK_ItemId, out var accepted);
+            return new InvoiceMatchLineResult(i.Id, i.FK_ItemId, i.Quantity, accepted, i.UnitCost, accepted == i.Quantity);
+        }).ToList();
+
+        var isMatched = lines.All(l => l.QuantityMatches);
+
+        return new InvoiceMatchResult(
+            poId, grnId, invoiceId, isMatched, lines,
+            "Compares PurchaseOrderItem.Quantity against GoodsReceiptItem.AcceptedQuantity only; " +
+            "invoice line comparison activates once Finance's Invoice entity (step 19) exists.");
+    }
+
+    /// <summary>
+    /// Records a Po/Grn(/invoice) variance and its resolution. Never silently adjusts anything except
+    /// when the resolution explicitly requests a retroactive UnitCost adjustment on a named line.
+    /// </summary>
+    public async Task<InvoiceVarianceResolutionResponse?> ResolveInvoiceVarianceAsync(Guid poId, ResolveInvoiceVarianceRequest request, CancellationToken ct = default)
+    {
+        var po = await repo.GetByIdAsync(poId);
+        if (po is null || !po.IsActive) return null;
+
+        if (request.AdjustedUnitCost.HasValue)
+        {
+            if (!request.PurchaseOrderItemId.HasValue)
+                throw new InvalidOperationException("PurchaseOrderItemId is required when adjusting UnitCost.");
+
+            var line = po.Items.FirstOrDefault(i => i.Id == request.PurchaseOrderItemId.Value && i.IsActive)
+                ?? throw new InvalidOperationException("Purchase order line not found on this Po.");
+
+            line.UnitCost = request.AdjustedUnitCost.Value;
+
+            await uow.BeginAsync(ct);
+            try { repo.Update(po); await uow.CommitAsync(ct); }
+            catch { await uow.RollbackAsync(ct); throw; }
+        }
+
+        return new InvoiceVarianceResolutionResponse(poId, request.Variance, request.Resolution, DateTime.Now);
+    }
+}