diff --git a/.changeset/72-project-business-context.md b/.changeset/72-project-business-context.md
new file mode 100644
index 000000000..cfa52862d
--- /dev/null
+++ b/.changeset/72-project-business-context.md
@@ -0,0 +1,5 @@
+---
+type: Added
+pr: 756
+---
+**Optional `## Business Context` section in the PROJECT.md template** — a four-field block (Customer, Revenue model, Success metric, Strategy notes) for monetized or customer-facing projects, positioned between Core Value and Requirements. Optional by default (an HTML comment tells non-business projects to delete it), capped at four one-line fields to stay a constraint reference rather than a business plan, and reviewed at each milestone by `/gsd-complete-milestone` when present. (#72)
diff --git a/docs/reference/planning-artifacts.md b/docs/reference/planning-artifacts.md
index 41ef84113..45e73360b 100644
--- a/docs/reference/planning-artifacts.md
+++ b/docs/reference/planning-artifacts.md
@@ -51,6 +51,8 @@ The `.planning/` directory is GSD Core's shared memory for a project. Every work
 | **Produced by** | `/gsd-new-project` (initial creation); updated by `/gsd-complete-milestone` as decisions are validated. |
 | **Consumed by** | All planning workflows; `gsd-phase-researcher`, `gsd-planner` (context); `discuss-phase` (prior decisions); `gsd-plan-checker` (project constraints). |
 
+Includes an optional `## Business Context` section (Customer, Revenue model, Success metric, Strategy notes) for monetized or customer-facing projects — four one-line fields that connect business outcomes to requirement prioritization. It is deleted for internal tools, experiments, or meta workspaces, and reviewed at each milestone by `/gsd-complete-milestone` when present.
+
 ### `ROADMAP.md`
 
 | | |
diff --git a/gsd-core/templates/project.md b/gsd-core/templates/project.md
index 37a986c70..a78c5c220 100644
--- a/gsd-core/templates/project.md
+++ b/gsd-core/templates/project.md
@@ -17,6 +17,15 @@ Use the user's language and framing. Update whenever reality drifts from this de
 [The ONE thing that matters most. If everything else fails, this must work.
 One sentence that drives prioritization when tradeoffs arise.]
 
+## Business Context
+
+<!-- OPTIONAL — only for monetized or customer-facing projects. Delete this section otherwise. -->
+
+- **Customer**: [Who pays / who uses — one line]
+- **Revenue model**: [How it makes money — one line]
+- **Success metric**: [The number that matters — one line]
+- **Strategy notes**: [Link to external strategy doc, if any]
+
 ## Requirements
 
 ### Validated
@@ -83,6 +92,13 @@ Common types: Tech stack, Timeline, Budget, Dependencies, Compatibility, Perform
 - Drives prioritization when tradeoffs arise
 - Rarely changes; if it does, it's a significant pivot
 
+**Business Context:**
+- Optional — only for monetized or customer-facing projects
+- Delete the entire section for internal tools, experiments, or meta workspaces
+- 4 fields max, one line each — a constraint reference, not a business plan
+- Use **Strategy notes** to link out to a dedicated strategy doc rather than duplicating it here
+- Informs requirement prioritization: features serving the customer/revenue model come first
+
 **Requirements — Validated:**
 - Requirements that shipped and proved valuable
 - Format: `- ✓ [Requirement] — [version/phase]`
@@ -140,8 +156,9 @@ and implemented by workflows/transition.md and workflows/complete-milestone.md.
 **After each milestone:**
 1. Full review of all sections
 2. Core Value check — still the right priority?
-3. Audit Out of Scope — reasons still valid?
-4. Update Context with current state (users, feedback, metrics)
+3. Business Context check (if present) — customer, revenue model, success metric still accurate?
+4. Audit Out of Scope — reasons still valid?
+5. Update Context with current state (users, feedback, metrics)
 
 </evolution>
 
diff --git a/gsd-core/workflows/complete-milestone.md b/gsd-core/workflows/complete-milestone.md
index 029e6e298..a7755945c 100644
--- a/gsd-core/workflows/complete-milestone.md
+++ b/gsd-core/workflows/complete-milestone.md
@@ -245,7 +245,12 @@ cat .planning/phases/*-*/*-SUMMARY.md
    - Still the right priority? Did shipping reveal a different core value?
    - Update if the ONE thing has shifted
 
-3. **Requirements audit:**
+3. **Business Context check (only if the section is present):**
+   - Skip entirely if PROJECT.md has no `## Business Context` section
+   - Customer, revenue model, and success metric still accurate after shipping?
+   - Update any field that drifted; refresh the linked strategy doc reference if it moved
+
+4. **Requirements audit:**
 
    **Validated section:**
    - All Active requirements shipped this milestone → Move to Validated
@@ -261,17 +266,17 @@ cat .planning/phases/*-*/*-SUMMARY.md
    - Remove irrelevant items
    - Add requirements invalidated during milestone
 
-4. **Context update:**
+5. **Context update:**
    - Current codebase state (LOC, tech stack)
    - User feedback themes (if any)
    - Known issues or technical debt
 
-5. **Key Decisions audit:**
+6. **Key Decisions audit:**
    - Extract all decisions from milestone phase summaries
    - Add to Key Decisions table with outcomes
    - Mark ✓ Good, ⚠️ Revisit, or — Pending
 
-6. **Constraints check:**
+7. **Constraints check:**
    - Any constraints changed during development? Update as needed
 
 Update PROJECT.md inline. Update "Last updated" footer:
@@ -355,6 +360,7 @@ Initial user testing showed demand for shape tools.
 
 - [ ] "What This Is" reviewed and updated if needed
 - [ ] Core Value verified as still correct
+- [ ] Business Context checked (or confirmed absent)
 - [ ] All shipped requirements moved to Validated
 - [ ] New requirements added to Active for next milestone
 - [ ] Out of Scope reasoning audited
diff --git a/tests/enh-72-business-context.test.cjs b/tests/enh-72-business-context.test.cjs
new file mode 100644
index 000000000..b58b7007e
--- /dev/null
+++ b/tests/enh-72-business-context.test.cjs
@@ -0,0 +1,96 @@
+// allow-test-rule: source-text-is-the-product
+// The PROJECT.md template + complete-milestone workflow .md ARE the product surface
+// the runtime loads; asserting on their text tests the deployed contract directly.
+/**
+ * Enhancement #72 — optional Business Context section in the PROJECT.md template.
+ *
+ * Contract tests over the product-text surfaces (template + milestone workflow .md):
+ * the template offers a Business Context section that is explicitly OPTIONAL, capped
+ * at the four approved one-line fields, and the milestone evolution review treats it
+ * as conditional so non-business projects that deleted it are never forced to review it.
+ */
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+
+const TEMPLATE = path.join(__dirname, '..', 'gsd-core', 'templates', 'project.md');
+const COMPLETE_MILESTONE = path.join(__dirname, '..', 'gsd-core', 'workflows', 'complete-milestone.md');
+
+function parseTemplateContract(content) {
+  const lines = content.split(/\r?\n/);
+  const lower = content.toLowerCase();
+  // The Business Context block lives between its heading and the next "## " heading.
+  const startIdx = lines.findIndex(l => l.trim() === '## Business Context');
+  let sectionBody = '';
+  if (startIdx !== -1) {
+    const rest = lines.slice(startIdx + 1);
+    const endOffset = rest.findIndex(l => l.startsWith('## '));
+    sectionBody = (endOffset === -1 ? rest : rest.slice(0, endOffset)).join('\n');
+  }
+  const fieldOf = (label) => new RegExp(`^- \\*\\*${label}\\*\\*:`, 'm').test(sectionBody);
+  return {
+    hasSection: startIdx !== -1,
+    // Optional-by-default: an HTML comment tells non-business projects to delete it.
+    hasOptionalMarker: /<!--\s*OPTIONAL/i.test(sectionBody) && /delete this section/i.test(sectionBody),
+    fields: {
+      customer: fieldOf('Customer'),
+      revenueModel: fieldOf('Revenue model'),
+      successMetric: fieldOf('Success metric'),
+      strategyNotes: fieldOf('Strategy notes'),
+    },
+    fieldCount: (sectionBody.match(/^- \*\*/gm) || []).length,
+    // Positioned between Core Value and Requirements.
+    orderedBetweenCoreValueAndRequirements:
+      lower.indexOf('## core value') < lower.indexOf('## business context') &&
+      lower.indexOf('## business context') < lower.indexOf('## requirements'),
+    hasGuidelinesEntry: /\*\*Business Context:\*\*/.test(content),
+  };
+}
+
+function parseMilestoneContract(content) {
+  const lower = content.toLowerCase();
+  const lines = content.split(/\r?\n/);
+  const reviewLine = lines.find(l =>
+    l.toLowerCase().includes('business context') &&
+    (l.toLowerCase().includes('if present') || l.toLowerCase().includes('only if')),
+  );
+  return {
+    mentionsBusinessContext: lower.includes('business context'),
+    hasConditionalReview: Boolean(reviewLine),
+  };
+}
+
+describe('enhancement #72 — Business Context template section', () => {
+  const tpl = parseTemplateContract(fs.readFileSync(TEMPLATE, 'utf-8'));
+
+  test('template includes a Business Context section', () => {
+    assert.ok(tpl.hasSection, 'template must contain a "## Business Context" section');
+  });
+
+  test('section is marked OPTIONAL with delete-for-non-business guidance', () => {
+    assert.ok(tpl.hasOptionalMarker, 'section must carry an OPTIONAL HTML comment telling non-business projects to delete it');
+  });
+
+  test('section carries exactly the four approved one-line fields', () => {
+    assert.ok(tpl.fields.customer, 'missing **Customer** field');
+    assert.ok(tpl.fields.revenueModel, 'missing **Revenue model** field');
+    assert.ok(tpl.fields.successMetric, 'missing **Success metric** field');
+    assert.ok(tpl.fields.strategyNotes, 'missing **Strategy notes** field');
+    assert.strictEqual(tpl.fieldCount, 4, 'section is capped at four fields (constraint reference, not a business plan)');
+  });
+
+  test('section is positioned between Core Value and Requirements', () => {
+    assert.ok(tpl.orderedBetweenCoreValueAndRequirements, 'Business Context must sit between Core Value and Requirements');
+  });
+
+  test('guidelines document the Business Context section', () => {
+    assert.ok(tpl.hasGuidelinesEntry, 'guidelines block must include a **Business Context:** entry');
+  });
+
+  test('milestone evolution reviews Business Context only when present', () => {
+    const ms = parseMilestoneContract(fs.readFileSync(COMPLETE_MILESTONE, 'utf-8'));
+    assert.ok(ms.mentionsBusinessContext, 'complete-milestone must mention Business Context in its review');
+    assert.ok(ms.hasConditionalReview, 'the Business Context milestone review must be conditional on the section being present');
+  });
+});