diff --git a/CHANGELOG.md b/CHANGELOG.md
index 68b9f7f..031c511 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ This file is the running release and change log for CODEXIUM. Keep it updated wh
 
 ### Added
 
+- Reverse project visibility on quote and sales-order detail pages, purchase-order header project linkage, sales-order-driven project auto-derivation for new work orders and purchase orders, quote-to-sales-order project carry-through during conversion, and migration backfill for existing work orders and purchase orders linked through project sales orders
 - Finance module with customer-payment posting against sales orders, finance costing assumptions, sales-order cash/spend ledger rollups, manufacturing cost snapshots, and CapEx tracking for equipment, tooling, and consumables
 - Inventory-backed shipment picking from shipment detail pages, including sales-order line remaining-quantity visibility, warehouse/location source selection, issued-stock posting, and shipment pick history
 - Project cockpit section on project detail pages for commercial, supply, execution, delivery, purchasing, readiness-risk, and project cost snapshot rollups, plus direct launch paths into prefilled work-order and purchase-order follow-through and a chronological project activity timeline
diff --git a/README.md b/README.md
index 5ab2a59..c31294a 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,7 @@ Current foundation scope includes:
 - branded quote, sales-order, and purchase-order PDFs through the shared backend document pipeline
 - purchase-order supporting documents for vendor invoices, acknowledgements, certifications, and backup files
 - shipping shipments linked to sales orders with inventory-backed picking, stock issue posting, packing slips, shipping labels, bills of lading, and logistics attachments
-- projects with customer/commercial/shipment linkage, owners, due dates, milestones, rollups, notes, and attachments
+- projects with customer/commercial/shipment linkage, owners, due dates, milestones, rollups, notes, attachments, reverse-linked quote/sales-order visibility, and downstream project-context carry-through into generated work orders and purchase orders
 - manufacturing work orders with project linkage, station-based operation templates, editable station calendars/capacity settings, calendar-aware operation scheduling, operation execution controls, operator assignment, timer-based and manual labor posting, material issue posting, completion posting, operation rescheduling, and work-order attachments
 - planning workbench with live project/manufacturing schedule data, exception rail, heatmap load view, agenda view, focus drawer, station load grouping, readiness filters, overload visibility, inline dispatch actions, planner-side operation rebalance controls including station-to-station moves, and station-lane drag scheduling
 - sales-order demand planning with multi-level BOM explosion, stock/open-supply netting, and build/buy recommendations
@@ -116,6 +116,7 @@ Current interactions:
 
 - CRM: each project should link to a customer account and relevant contacts
 - Sales: quotes and sales orders can already attach to projects
+- Sales workflow now also exposes the reverse project link on quote and sales-order detail pages, and quote conversion carries linked project context forward into the created sales order
 - Shipping: shipments tied to project deliverables are visible from the project record
 - Dashboard: projects now contribute status, risk, backlog, and overdue widgets
 - Detail/List UX: projects now surface milestone progress and linked execution rollups
@@ -123,8 +124,8 @@ Current interactions:
 Next expansion areas:
 
 - Inventory: projects should reference item/BOM scope and later expose shortages or allocations
-- Purchasing: project material demand is now visible through linked PO, receipt, vendor, and outstanding-supply rollups, and should later expand into project-side purchasing actions
-- Manufacturing: work orders should link back to projects without turning projects into the manufacturing module
+- Purchasing: project material demand is now visible through linked PO, receipt, vendor, and outstanding-supply rollups, and purchase orders now persist header-level project context derived from linked sales demand or explicit project selection
+- Manufacturing: work orders already auto-link back to the project when the originating sales order belongs to a project, without turning projects into the manufacturing module
 - Planning: project milestones and execution dates should feed workbench scheduling, dependency views, and richer planner drilldowns
 
 ## Manufacturing Direction
diff --git a/SHIPPED.md b/SHIPPED.md
index b047fb3..20b5746 100644
--- a/SHIPPED.md
+++ b/SHIPPED.md
@@ -35,6 +35,7 @@ This file tracks roadmap phases, slices, and major foundations that have already
 - Packing-slip, shipping-label, and bill-of-lading PDF rendering for shipments
 - Logistics attachments directly on shipment records
 - Projects foundation with customer, quote, sales-order, shipment, owner, due-date, notes, and attachment linkage
+- Reverse project linkage visibility on quote and sales-order detail pages, plus project-context carry-through into generated work orders and purchase orders with sales-order-driven backfill for existing records
 - Project milestones and project-side milestone/work-order rollups
 - Project cockpit section on detail pages for commercial, supply, execution, delivery, purchasing, readiness-risk, and cost-snapshot visibility, with direct launch paths into prefilled project work orders and demand-linked purchase orders plus a project activity timeline
 - Project list/detail/create/edit workflows and dashboard program widgets
@@ -78,6 +79,7 @@ This file tracks roadmap phases, slices, and major foundations that have already
 - Project records with customer linkage, status, owner, priority, due dates, milestones, and notes
 - Project milestone status tracking and project-side milestone/work-order rollups
 - Project-to-quote, sales-order, and shipment linkage for delivery context
+- Quote-to-sales-order project carry-through plus reverse-linked project visibility from the sales workflow
 - Project attachments through the shared file pipeline
 - Project list/detail/create/edit flows and dashboard visibility
 
@@ -103,6 +105,7 @@ This file tracks roadmap phases, slices, and major foundations that have already
 - Netting against available stock, active reservations, open work orders, and open purchase orders
 - Build and buy recommendations surfaced directly from the sales-order workflow
 - Prefilled work-order and purchase-order draft generation launched from demand-planning recommendations
+- Generated work orders and purchase orders now auto-carry linked project context when demand traces back to a project-linked sales order
 - Shared shortage and readiness rollups surfaced across dashboard, planning, project, purchasing, and manufacturing views
 - Preferred-vendor sourcing on inventory items for buy-side planning defaults
 - Pegged work-order and purchase-order supply links back to originating sales demand
diff --git a/client/src/modules/purchasing/PurchaseDetailPage.tsx b/client/src/modules/purchasing/PurchaseDetailPage.tsx
index 4863341..d18152e 100644
--- a/client/src/modules/purchasing/PurchaseDetailPage.tsx
+++ b/client/src/modules/purchasing/PurchaseDetailPage.tsx
@@ -427,7 +427,18 @@ export function PurchaseDetailPage() {
           </dl>
         </article>
         <article className="rounded-[20px] border border-line/70 bg-surface/90 p-4 shadow-panel 2xl:p-5">
-          <p className="text-xs font-semibold uppercase tracking-[0.24em] text-muted">Notes</p>
+          <p className="text-xs font-semibold uppercase tracking-[0.24em] text-muted">Project Link</p>
+          {activeDocument.projectId ? (
+            <div className="mt-3 space-y-2">
+              <Link to={`/projects/${activeDocument.projectId}`} className="inline-flex items-center rounded-2xl border border-line/70 px-3 py-2 text-sm font-semibold text-text hover:bg-page/70">
+                {activeDocument.projectNumber} / {activeDocument.projectName}
+              </Link>
+              <p className="text-sm text-muted">This purchase order is linked to the project context used by project cockpit and downstream rollups.</p>
+            </div>
+          ) : (
+            <p className="mt-3 text-sm text-muted">No linked project is currently attached to this purchase order.</p>
+          )}
+          <p className="mt-5 text-xs font-semibold uppercase tracking-[0.24em] text-muted">Notes</p>
           <p className="mt-3 whitespace-pre-line text-sm leading-6 text-text">{activeDocument.notes || "No notes recorded for this document."}</p>
         </article>
       </div>
diff --git a/client/src/modules/purchasing/PurchaseFormPage.tsx b/client/src/modules/purchasing/PurchaseFormPage.tsx
index 57d5ce7..d2fa391 100644
--- a/client/src/modules/purchasing/PurchaseFormPage.tsx
+++ b/client/src/modules/purchasing/PurchaseFormPage.tsx
@@ -14,6 +14,9 @@ export function PurchaseFormPage({ mode }: { mode: "create" | "edit" }) {
   const { orderId } = useParams();
   const [searchParams] = useSearchParams();
   const seededVendorId = searchParams.get("vendorId");
+  const seededProjectId = searchParams.get("projectId");
+  const seededProjectNumber = searchParams.get("projectNumber");
+  const seededProjectName = searchParams.get("projectName");
   const planningOrderId = searchParams.get("planningOrderId");
   const selectedPlanningItemId = searchParams.get("itemId");
   const [form, setForm] = useState<PurchaseOrderInput>(emptyPurchaseOrderInput);
@@ -57,6 +60,12 @@ export function PurchaseFormPage({ mode }: { mode: "create" | "edit" }) {
     api.getInventoryItemOptions(token).then((options) => setItemOptions(options.filter((option: InventoryItemOptionDto) => option.isPurchasable))).catch(() => setItemOptions([]));
   }, [mode, seededVendorId, token]);
 
+  useEffect(() => {
+    if (mode === "create" && seededProjectId) {
+      setForm((current) => ({ ...current, projectId: current.projectId || seededProjectId }));
+    }
+  }, [mode, seededProjectId]);
+
   useEffect(() => {
     if (!token || mode !== "create" || !planningOrderId || itemOptions.length === 0) {
       return;
@@ -103,6 +112,7 @@ export function PurchaseFormPage({ mode }: { mode: "create" | "edit" }) {
         setForm((current) => ({
           ...current,
           vendorId: current.vendorId || autoVendorId || "",
+          projectId: current.projectId || seededProjectId || null,
           notes: current.notes || `Demand-planning recommendation from sales order ${planning.documentNumber}.`,
           lines: current.lines.length > 0 ? current.lines : recommendedLines,
         }));
@@ -124,7 +134,7 @@ export function PurchaseFormPage({ mode }: { mode: "create" | "edit" }) {
       .catch(() => {
         setStatus("Unable to load demand-planning recommendations.");
       });
-  }, [itemOptions, mode, planningOrderId, seededVendorId, selectedPlanningItemId, token, vendors]);
+  }, [itemOptions, mode, planningOrderId, seededProjectId, seededVendorId, selectedPlanningItemId, token, vendors]);
 
   useEffect(() => {
     if (!token || mode !== "edit" || !orderId) {
@@ -135,6 +145,7 @@ export function PurchaseFormPage({ mode }: { mode: "create" | "edit" }) {
       .then((document) => {
         setForm({
           vendorId: document.vendorId,
+          projectId: document.projectId,
           status: document.status,
           issueDate: document.issueDate,
           taxPercent: document.taxPercent,
@@ -341,6 +352,19 @@ export function PurchaseFormPage({ mode }: { mode: "create" | "edit" }) {
             <input type="date" value={form.issueDate.slice(0, 10)} onChange={(event) => updateField("issueDate", new Date(event.target.value).toISOString())} className="w-full rounded-2xl border border-line/70 bg-page px-2 py-2 text-text outline-none transition focus:border-brand" />
           </label>
         </div>
+        <div className="rounded-[18px] border border-line/70 bg-page/60 px-3 py-3 text-sm">
+          <div className="text-xs font-semibold uppercase tracking-[0.16em] text-muted">Linked Project</div>
+          <div className="mt-2 font-semibold text-text">
+            {mode === "edit"
+              ? (form.projectId ? "Project context saved on this purchase order." : "No project linked.")
+              : (seededProjectId ? `${seededProjectNumber || "Project"}${seededProjectName ? ` - ${seededProjectName}` : ""}` : "Will auto-link from sales-order demand when possible.")}
+          </div>
+          <div className="mt-1 text-xs text-muted">
+            {mode === "edit"
+              ? "This header link is used for downstream project cockpit and finance rollups."
+              : "Generated purchasing from a project-linked sales order will carry project context automatically."}
+          </div>
+        </div>
         <label className="block">
           <span className="mb-2 block text-sm font-semibold text-text">Notes</span>
           <textarea value={form.notes} onChange={(event) => updateField("notes", event.target.value)} rows={3} className="w-full rounded-[18px] border border-line/70 bg-page px-2 py-2 text-text outline-none transition focus:border-brand" />
diff --git a/client/src/modules/purchasing/config.ts b/client/src/modules/purchasing/config.ts
index 95b4fa1..53886a4 100644
--- a/client/src/modules/purchasing/config.ts
+++ b/client/src/modules/purchasing/config.ts
@@ -22,6 +22,7 @@ export const purchaseStatusPalette: Record<PurchaseOrderStatus, string> = {
 
 export const emptyPurchaseOrderInput: PurchaseOrderInput = {
   vendorId: "",
+  projectId: null,
   status: "DRAFT",
   issueDate: new Date().toISOString(),
   taxPercent: 0,
diff --git a/client/src/modules/sales/SalesDetailPage.tsx b/client/src/modules/sales/SalesDetailPage.tsx
index 53ced04..4c91e65 100644
--- a/client/src/modules/sales/SalesDetailPage.tsx
+++ b/client/src/modules/sales/SalesDetailPage.tsx
@@ -173,6 +173,9 @@ export function SalesDetailPage({ entity }: { entity: SalesDocumentEntity }) {
       status: "DRAFT",
       notes: `Generated from sales order ${activeDocument.documentNumber} demand planning.`,
     });
+    if (activeDocument.linkedProjectId) {
+      params.set("projectId", activeDocument.linkedProjectId);
+    }
 
     return `/manufacturing/work-orders/new?${params.toString()}`;
   }
@@ -186,6 +189,15 @@ export function SalesDetailPage({ entity }: { entity: SalesDocumentEntity }) {
     if (vendorId) {
       params.set("vendorId", vendorId);
     }
+    if (activeDocument.linkedProjectId) {
+      params.set("projectId", activeDocument.linkedProjectId);
+    }
+    if (activeDocument.linkedProjectNumber) {
+      params.set("projectNumber", activeDocument.linkedProjectNumber);
+    }
+    if (activeDocument.linkedProjectName) {
+      params.set("projectName", activeDocument.linkedProjectName);
+    }
 
     return `/purchasing/orders/new?${params.toString()}`;
   }
@@ -521,7 +533,18 @@ export function SalesDetailPage({ entity }: { entity: SalesDocumentEntity }) {
           </dl>
         </article>
         <article className="rounded-[20px] border border-line/70 bg-surface/90 p-4 shadow-panel 2xl:p-5">
-          <p className="text-xs font-semibold uppercase tracking-[0.24em] text-muted">Notes</p>
+          <p className="text-xs font-semibold uppercase tracking-[0.24em] text-muted">Project Link</p>
+          {activeDocument.linkedProjectId ? (
+            <div className="mt-3 space-y-2">
+              <Link to={`/projects/${activeDocument.linkedProjectId}`} className="inline-flex items-center rounded-2xl border border-line/70 px-3 py-2 text-sm font-semibold text-text hover:bg-page/70">
+                {activeDocument.linkedProjectNumber} / {activeDocument.linkedProjectName}
+              </Link>
+              <p className="text-sm text-muted">This {entity === "quote" ? "quote" : "sales order"} is already linked to a project, and downstream WO/PO launches will carry that project context.</p>
+            </div>
+          ) : (
+            <p className="mt-3 text-sm text-muted">No linked project is currently attached to this {entity === "quote" ? "quote" : "sales order"}.</p>
+          )}
+          <p className="mt-5 text-xs font-semibold uppercase tracking-[0.24em] text-muted">Notes</p>
           <p className="mt-3 whitespace-pre-line text-sm leading-6 text-text">{activeDocument.notes || "No notes recorded for this document."}</p>
         </article>
       </div>
diff --git a/server/prisma/migrations/20260318014000_project_linkage_backfill/migration.sql b/server/prisma/migrations/20260318014000_project_linkage_backfill/migration.sql
new file mode 100644
index 0000000..c929edc
--- /dev/null
+++ b/server/prisma/migrations/20260318014000_project_linkage_backfill/migration.sql
@@ -0,0 +1,38 @@
+ALTER TABLE "PurchaseOrder" ADD COLUMN "projectId" TEXT REFERENCES "Project"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+CREATE INDEX "PurchaseOrder_projectId_issueDate_idx" ON "PurchaseOrder"("projectId", "issueDate");
+
+UPDATE "WorkOrder"
+SET "projectId" = (
+  SELECT "Project"."id"
+  FROM "Project"
+  WHERE "Project"."salesOrderId" = "WorkOrder"."salesOrderId"
+  ORDER BY "Project"."createdAt" ASC
+  LIMIT 1
+)
+WHERE "projectId" IS NULL
+  AND "salesOrderId" IS NOT NULL
+  AND EXISTS (
+    SELECT 1
+    FROM "Project"
+    WHERE "Project"."salesOrderId" = "WorkOrder"."salesOrderId"
+  );
+
+UPDATE "PurchaseOrder"
+SET "projectId" = (
+  SELECT "Project"."id"
+  FROM "PurchaseOrderLine"
+  INNER JOIN "Project" ON "Project"."salesOrderId" = "PurchaseOrderLine"."salesOrderId"
+  WHERE "PurchaseOrderLine"."purchaseOrderId" = "PurchaseOrder"."id"
+    AND "PurchaseOrderLine"."salesOrderId" IS NOT NULL
+  ORDER BY "Project"."createdAt" ASC
+  LIMIT 1
+)
+WHERE "projectId" IS NULL
+  AND EXISTS (
+    SELECT 1
+    FROM "PurchaseOrderLine"
+    INNER JOIN "Project" ON "Project"."salesOrderId" = "PurchaseOrderLine"."salesOrderId"
+    WHERE "PurchaseOrderLine"."purchaseOrderId" = "PurchaseOrder"."id"
+      AND "PurchaseOrderLine"."salesOrderId" IS NOT NULL
+  );
diff --git a/server/prisma/schema.prisma b/server/prisma/schema.prisma
index 697dc61..da49bdf 100644
--- a/server/prisma/schema.prisma
+++ b/server/prisma/schema.prisma
@@ -618,6 +618,7 @@ model Project {
   shipment      Shipment? @relation(fields: [shipmentId], references: [id], onDelete: SetNull)
   owner         User? @relation("ProjectOwner", fields: [ownerId], references: [id], onDelete: SetNull)
   workOrders    WorkOrder[]
+  purchaseOrders PurchaseOrder[]
   milestones    ProjectMilestone[]
 
   @@index([customerId, createdAt])
@@ -864,6 +865,7 @@ model PurchaseOrder {
   id             String   @id @default(cuid())
   documentNumber String   @unique
   vendorId       String
+  projectId      String?
   status         String
   issueDate      DateTime
   taxPercent     Float    @default(0)
@@ -872,10 +874,13 @@ model PurchaseOrder {
   createdAt      DateTime @default(now())
   updatedAt      DateTime @updatedAt
   vendor         Vendor   @relation(fields: [vendorId], references: [id], onDelete: Restrict)
+  project        Project? @relation(fields: [projectId], references: [id], onDelete: SetNull)
   lines          PurchaseOrderLine[]
   receipts       PurchaseReceipt[]
   revisions      PurchaseOrderRevision[]
   capexEntries   CapexEntry[]
+
+  @@index([projectId, issueDate])
 }
 
 model PurchaseOrderLine {
diff --git a/server/src/modules/manufacturing/service.ts b/server/src/modules/manufacturing/service.ts
index aa75fc9..0ba1369 100644
--- a/server/src/modules/manufacturing/service.ts
+++ b/server/src/modules/manufacturing/service.ts
@@ -868,15 +868,18 @@ async function validateWorkOrderInput(payload: WorkOrderInput) {
     return { ok: false as const, reason: "Build item must have at least one station operation before a work order can be created." };
   }
 
+  let projectSalesOrderId: string | null = null;
   if (payload.projectId) {
     const project = await prisma.project.findUnique({
       where: { id: payload.projectId },
-      select: { id: true },
+      select: { id: true, salesOrderId: true },
     });
 
     if (!project) {
       return { ok: false as const, reason: "Linked project was not found." };
     }
+
+    projectSalesOrderId = project.salesOrderId ?? null;
   }
 
   if (payload.salesOrderId) {
@@ -888,6 +891,10 @@ async function validateWorkOrderInput(payload: WorkOrderInput) {
     if (!salesOrder) {
       return { ok: false as const, reason: "Linked sales order was not found." };
     }
+
+    if (projectSalesOrderId && projectSalesOrderId !== payload.salesOrderId) {
+      return { ok: false as const, reason: "Linked project does not match the selected sales order." };
+    }
   }
 
   if (payload.salesOrderLineId) {
@@ -928,6 +935,28 @@ async function validateWorkOrderInput(payload: WorkOrderInput) {
   return { ok: true as const };
 }
 
+async function deriveProjectIdForWorkOrder(payload: WorkOrderInput) {
+  if (payload.projectId) {
+    return payload.projectId;
+  }
+
+  if (!payload.salesOrderId) {
+    return null;
+  }
+
+  const project = await prisma.project.findFirst({
+    where: {
+      salesOrderId: payload.salesOrderId,
+    },
+    orderBy: [{ createdAt: "asc" }],
+    select: {
+      id: true,
+    },
+  });
+
+  return project?.id ?? null;
+}
+
 export async function listManufacturingItemOptions(): Promise<ManufacturingItemOptionDto[]> {
   const items = await prisma.inventoryItem.findMany({
     where: {
@@ -1158,13 +1187,14 @@ export async function createWorkOrder(payload: WorkOrderInput, actorId?: string
   if (!validated.ok) {
     return { ok: false as const, reason: validated.reason };
   }
+  const derivedProjectId = await deriveProjectIdForWorkOrder(payload);
 
   const workOrderNumber = await nextWorkOrderNumber();
   const created = await workOrderModel.create({
     data: {
       workOrderNumber,
       itemId: payload.itemId,
-      projectId: payload.projectId,
+      projectId: derivedProjectId,
       salesOrderId: payload.salesOrderId,
       salesOrderLineId: payload.salesOrderLineId,
       warehouseId: payload.warehouseId,
@@ -1223,12 +1253,13 @@ export async function updateWorkOrder(workOrderId: string, payload: WorkOrderInp
   if (!validated.ok) {
     return { ok: false as const, reason: validated.reason };
   }
+  const derivedProjectId = await deriveProjectIdForWorkOrder(payload);
 
   await workOrderModel.update({
     where: { id: workOrderId },
     data: {
       itemId: payload.itemId,
-      projectId: payload.projectId,
+      projectId: derivedProjectId,
       salesOrderId: payload.salesOrderId,
       salesOrderLineId: payload.salesOrderLineId,
       warehouseId: payload.warehouseId,
diff --git a/server/src/modules/purchasing/router.ts b/server/src/modules/purchasing/router.ts
index 64226e5..a8c7b89 100644
--- a/server/src/modules/purchasing/router.ts
+++ b/server/src/modules/purchasing/router.ts
@@ -29,6 +29,7 @@ const purchaseLineSchema = z.object({
 
 const purchaseOrderSchema = z.object({
   vendorId: z.string().trim().min(1),
+  projectId: z.string().trim().min(1).nullable().optional(),
   status: z.enum(purchaseOrderStatuses),
   issueDate: z.string().datetime(),
   taxPercent: z.number().min(0).max(100),
diff --git a/server/src/modules/purchasing/service.ts b/server/src/modules/purchasing/service.ts
index 87082e3..761e92c 100644
--- a/server/src/modules/purchasing/service.ts
+++ b/server/src/modules/purchasing/service.ts
@@ -126,6 +126,11 @@ type PurchaseOrderRevisionRecord = {
 type PurchaseOrderRecord = {
   id: string;
   documentNumber: string;
+  project: {
+    id: string;
+    projectNumber: string;
+    name: string;
+  } | null;
   status: string;
   issueDate: Date;
   taxPercent: number;
@@ -145,6 +150,17 @@ type PurchaseOrderRecord = {
   revisions: PurchaseOrderRevisionRecord[];
 };
 
+type NormalizedPurchaseLine = {
+  itemId: string;
+  salesOrderId: string | null;
+  salesOrderLineId: string | null;
+  description: string;
+  quantity: number;
+  unitOfMeasure: PurchaseLineInput["unitOfMeasure"];
+  unitCost: number;
+  position: number;
+};
+
 function roundMoney(value: number) {
   return Math.round(value * 100) / 100;
 }
@@ -322,6 +338,63 @@ async function validateLines(lines: PurchaseLineInput[]) {
   return { ok: true as const, lines: normalized };
 }
 
+async function resolvePurchaseOrderProjectId(projectId: string | null | undefined, lines: NormalizedPurchaseLine[]) {
+  let explicitProjectId = projectId ?? null;
+
+  if (explicitProjectId) {
+    const project = await prisma.project.findUnique({
+      where: { id: explicitProjectId },
+      select: {
+        id: true,
+        salesOrderId: true,
+      },
+    });
+    if (!project) {
+      return { ok: false as const, reason: "Linked project was not found." };
+    }
+
+    const linkedSalesOrderIds = [...new Set(lines.flatMap((line) => (line.salesOrderId ? [line.salesOrderId] : [])))];
+    if (linkedSalesOrderIds.length > 0 && project.salesOrderId && linkedSalesOrderIds.some((salesOrderId) => salesOrderId !== project.salesOrderId)) {
+      return { ok: false as const, reason: "Linked project does not match the sales-order demand attached to this purchase order." };
+    }
+
+    return { ok: true as const, projectId: project.id };
+  }
+
+  const linkedSalesOrderIds = [...new Set(lines.flatMap((line) => (line.salesOrderId ? [line.salesOrderId] : [])))];
+  if (linkedSalesOrderIds.length === 0) {
+    return { ok: true as const, projectId: null };
+  }
+
+  const matchingProjects = await prisma.project.findMany({
+    where: {
+      salesOrderId: {
+        in: linkedSalesOrderIds,
+      },
+    },
+    select: {
+      id: true,
+      salesOrderId: true,
+      createdAt: true,
+    },
+    orderBy: [{ createdAt: "asc" }],
+  });
+
+  const projectBySalesOrderId = new Map<string, string>();
+  for (const project of matchingProjects) {
+    if (project.salesOrderId && !projectBySalesOrderId.has(project.salesOrderId)) {
+      projectBySalesOrderId.set(project.salesOrderId, project.id);
+    }
+  }
+
+  const derivedProjectIds = [...new Set(linkedSalesOrderIds.map((salesOrderId) => projectBySalesOrderId.get(salesOrderId)).filter((value): value is string => Boolean(value)))];
+  if (derivedProjectIds.length > 1) {
+    return { ok: false as const, reason: "Purchase orders can only auto-link to one project. Split the document or set the project intentionally." };
+  }
+
+  return { ok: true as const, projectId: derivedProjectIds[0] ?? null };
+}
+
 function mapPurchaseOrder(record: PurchaseOrderRecord): PurchaseOrderDetailDto {
   const receivedByLineId = new Map<string, number>();
 
@@ -370,6 +443,9 @@ function mapPurchaseOrder(record: PurchaseOrderRecord): PurchaseOrderDetailDto {
     documentNumber: record.documentNumber,
     vendorId: record.vendor.id,
     vendorName: record.vendor.name,
+    projectId: record.project?.id ?? null,
+    projectNumber: record.project?.projectNumber ?? null,
+    projectName: record.project?.name ?? null,
     vendorEmail: record.vendor.email,
     paymentTerms: record.vendor.paymentTerms,
     currencyCode: record.vendor.currencyCode,
@@ -487,6 +563,13 @@ const purchaseOrderInclude = Prisma.validator<Prisma.PurchaseOrderInclude>()({
       currencyCode: true,
     },
   },
+  project: {
+    select: {
+      id: true,
+      projectNumber: true,
+      name: true,
+    },
+  },
   lines: {
     include: {
       item: {
@@ -715,6 +798,9 @@ export async function listPurchaseOrders(filters: { q?: string; status?: Purchas
       documentNumber: detail.documentNumber,
       vendorId: detail.vendorId,
       vendorName: detail.vendorName,
+      projectId: detail.projectId,
+      projectNumber: detail.projectNumber,
+      projectName: detail.projectName,
       status: detail.status,
       subtotal: detail.subtotal,
       taxPercent: detail.taxPercent,
@@ -762,6 +848,11 @@ export async function createPurchaseOrder(payload: PurchaseOrderInput, actorId?:
     return { ok: false as const, reason: validatedLines.reason };
   }
 
+  const resolvedProject = await resolvePurchaseOrderProjectId(payload.projectId, validatedLines.lines);
+  if (!resolvedProject.ok) {
+    return { ok: false as const, reason: resolvedProject.reason };
+  }
+
   const vendor = await prisma.vendor.findUnique({
     where: { id: payload.vendorId },
     select: { id: true },
@@ -777,6 +868,7 @@ export async function createPurchaseOrder(payload: PurchaseOrderInput, actorId?:
     data: {
       documentNumber,
       vendorId: payload.vendorId,
+      projectId: resolvedProject.projectId,
       status: payload.status,
       issueDate: new Date(payload.issueDate),
       taxPercent: payload.taxPercent,
@@ -824,6 +916,11 @@ export async function updatePurchaseOrder(documentId: string, payload: PurchaseO
     return { ok: false as const, reason: validatedLines.reason };
   }
 
+  const resolvedProject = await resolvePurchaseOrderProjectId(payload.projectId, validatedLines.lines);
+  if (!resolvedProject.ok) {
+    return { ok: false as const, reason: resolvedProject.reason };
+  }
+
   const vendor = await prisma.vendor.findUnique({
     where: { id: payload.vendorId },
     select: { id: true },
@@ -837,6 +934,7 @@ export async function updatePurchaseOrder(documentId: string, payload: PurchaseO
     where: { id: documentId },
     data: {
       vendorId: payload.vendorId,
+      projectId: resolvedProject.projectId,
       status: payload.status,
       issueDate: new Date(payload.issueDate),
       taxPercent: payload.taxPercent,
diff --git a/server/src/modules/sales/service.ts b/server/src/modules/sales/service.ts
index 99d08ad..7fcf088 100644
--- a/server/src/modules/sales/service.ts
+++ b/server/src/modules/sales/service.ts
@@ -97,6 +97,12 @@ type SalesDocumentRecord = {
     firstName: string;
     lastName: string;
   } | null;
+  projects: Array<{
+    id: string;
+    projectNumber: string;
+    name: string;
+    createdAt: Date;
+  }>;
   revisions: RevisionRecord[];
   lines: SalesLineRecord[];
 };
@@ -279,6 +285,9 @@ function mapDocument(record: SalesDocumentRecord): SalesDocumentDetailDto {
     notes: record.notes,
     createdAt: record.createdAt.toISOString(),
     updatedAt: record.updatedAt.toISOString(),
+    linkedProjectId: record.projects[0]?.id ?? null,
+    linkedProjectNumber: record.projects[0]?.projectNumber ?? null,
+    linkedProjectName: record.projects[0]?.name ?? null,
     lineCount: lines.length,
     lines,
     revisions,
@@ -383,6 +392,15 @@ function buildInclude() {
         lastName: true,
       },
     },
+    projects: {
+      select: {
+        id: true,
+        projectNumber: true,
+        name: true,
+        createdAt: true,
+      },
+      orderBy: [{ createdAt: "asc" as const }],
+    },
     revisions: {
       include: {
         createdBy: {
@@ -799,6 +817,16 @@ export async function convertQuoteToSalesOrder(quoteId: string, userId?: string)
       select: { id: true },
     });
 
+    await tx.project.updateMany({
+      where: {
+        salesQuoteId: quoteId,
+        salesOrderId: null,
+      },
+      data: {
+        salesOrderId: created.id,
+      },
+    });
+
     return created.id;
   });
 
diff --git a/shared/src/purchasing/types.ts b/shared/src/purchasing/types.ts
index 49077ab..b769cbd 100644
--- a/shared/src/purchasing/types.ts
+++ b/shared/src/purchasing/types.ts
@@ -46,6 +46,9 @@ export interface PurchaseOrderSummaryDto {
   documentNumber: string;
   vendorId: string;
   vendorName: string;
+  projectId: string | null;
+  projectNumber: string | null;
+  projectName: string | null;
   status: PurchaseOrderStatus;
   subtotal: number;
   taxPercent: number;
@@ -70,6 +73,7 @@ export interface PurchaseOrderDetailDto extends PurchaseOrderSummaryDto {
 
 export interface PurchaseOrderInput {
   vendorId: string;
+  projectId?: string | null;
   status: PurchaseOrderStatus;
   issueDate: string;
   taxPercent: number;
diff --git a/shared/src/sales/types.ts b/shared/src/sales/types.ts
index 8704eed..875aefa 100644
--- a/shared/src/sales/types.ts
+++ b/shared/src/sales/types.ts
@@ -60,6 +60,9 @@ export interface SalesDocumentDetailDto extends SalesDocumentSummaryDto {
   notes: string;
   expiresAt: string | null;
   createdAt: string;
+  linkedProjectId: string | null;
+  linkedProjectNumber: string | null;
+  linkedProjectName: string | null;
   lines: SalesLineDto[];
   revisions: SalesDocumentRevisionDto[];
 }