diff --git a/README.md b/README.md
index 6fbb203..1269299 100644
--- a/README.md
+++ b/README.md
@@ -301,6 +301,15 @@ The helper lives in `app/lib/errors/index.ts`. Use `errorResponse(code, message,
 
 See `app/lib/api-version.ts` for the `toV2Stream()` conversion and `openapi.json` for the full OpenAPI 3.1 spec.
 
+## Organization Management API
+
+The following endpoints support multi-tenant organization management:
+
+- `POST /api/orgs/[orgId]/members`: Add a member to an organization (Owner-only).
+- `GET /api/orgs/[orgId]/members`: List organization members (Member-only).
+
+These endpoints require a valid JWT token obtained via `POST /api/auth/wallet` in the `Authorization: Bearer <token>` header.
+
 ## License
 
 MIT
diff --git a/app/api/orgs/[orgId]/members/route.test.ts b/app/api/orgs/[orgId]/members/route.test.ts
new file mode 100644
index 0000000..f8676d8
--- /dev/null
+++ b/app/api/orgs/[orgId]/members/route.test.ts
@@ -0,0 +1,53 @@
+import { GET, POST } from "./route";
+import { db } from "@/app/lib/db";
+import { NextRequest } from "next/server";
+
+// Mocking JWT verification in app/lib/auth
+jest.mock("jsonwebtoken", () => ({
+  verify: jest.fn((token) => {
+    if (token === "valid-owner-token") return { sub: "GATODH2T75IVFB7MG6ZKKIFPWFNVJBXVPUMTYV5ANT2O2ZWL7GSDZWNRW" };
+    if (token === "valid-member-token") return { sub: "other-wallet" };
+    throw new Error("Invalid token");
+  }),
+}));
+
+describe("Org Members API", () => {
+  const orgId = "org-1";
+
+  beforeEach(() => {
+    // Ensure DB is in a known state
+    db.members.set(`${orgId}:GATODH2T75IVFB7MG6ZKKIFPWFNVJBXVPUMTYV5ANT2O2ZWL7GSDZWNRW`, { orgId, walletAddress: "GATODH2T75IVFB7MG6ZKKIFPWFNVJBXVPUMTYV5ANT2O2ZWL7GSDZWNRW", role: "owner" });
+    db.members.set(`${orgId}:other-wallet`, { orgId, walletAddress: "other-wallet", role: "member" });
+  });
+
+  it("GET /:orgId/members - returns members for an authenticated member", async () => {
+    const req = new NextRequest(`http://localhost/api/orgs/${orgId}/members`, {
+      headers: { Authorization: "Bearer valid-member-token" },
+    });
+    const res = await GET(req, { params: Promise.resolve({ orgId }) });
+    expect(res.status).toBe(200);
+    const data = await res.json();
+    expect(data.data).toHaveLength(2);
+  });
+
+  it("POST /:orgId/members - allows owner to add a member", async () => {
+    const req = new NextRequest(`http://localhost/api/orgs/${orgId}/members`, {
+      method: "POST",
+      headers: { Authorization: "Bearer valid-owner-token", "Content-Type": "application/json" },
+      body: JSON.stringify({ walletAddress: "new-wallet" }),
+    });
+    const res = await POST(req, { params: Promise.resolve({ orgId }) });
+    expect(res.status).toBe(201);
+    expect(db.members.has(`${orgId}:new-wallet`)).toBe(true);
+  });
+
+  it("POST /:orgId/members - rejects non-owner", async () => {
+    const req = new NextRequest(`http://localhost/api/orgs/${orgId}/members`, {
+      method: "POST",
+      headers: { Authorization: "Bearer valid-member-token", "Content-Type": "application/json" },
+      body: JSON.stringify({ walletAddress: "attacker-wallet" }),
+    });
+    const res = await POST(req, { params: Promise.resolve({ orgId }) });
+    expect(res.status).toBe(403);
+  });
+});
diff --git a/app/api/orgs/[orgId]/members/route.ts b/app/api/orgs/[orgId]/members/route.ts
index 9970c7f..2713fb4 100644
--- a/app/api/orgs/[orgId]/members/route.ts
+++ b/app/api/orgs/[orgId]/members/route.ts
@@ -1,3 +1,35 @@
+import { NextResponse } from "next/server";
+import { tryAuthenticateRequest, createErrorResponse } from "@/app/lib/auth";
+import { db } from "@/app/lib/db";
+
+export async function GET(request: Request, { params }: { params: Promise<{ orgId: string }> }) {
+  const { orgId } = await params;
+  const auth = tryAuthenticateRequest(request);
+  if (auth.error) return createErrorResponse("UNAUTHORIZED", auth.error, 401);
+  const { walletAddress } = auth as { walletAddress: string };
+
+  const isMember = db.members.has(`${orgId}:${walletAddress}`);
+  if (!isMember) return createErrorResponse("FORBIDDEN", "You are not a member of this organization", 403);
+
+  const members = Array.from(db.members.values()).filter(m => m.orgId === orgId);
+  return NextResponse.json({ data: members });
+}
+
+export async function POST(request: Request, { params }: { params: Promise<{ orgId: string }> }) {
+  const { orgId } = await params;
+  const auth = tryAuthenticateRequest(request);
+  if (auth.error) return createErrorResponse("UNAUTHORIZED", auth.error, 401);
+  const { walletAddress } = auth as { walletAddress: string };
+
+  const org = db.orgs.get(orgId);
+  if (!org) return createErrorResponse("NOT_FOUND", "Organization not found", 404);
+
+  if (org.ownerWallet !== walletAddress) return createErrorResponse("FORBIDDEN", "Only the owner can add members", 403);
+
+  const { walletAddress: newMemberWallet } = await request.json();
+  db.members.set(`${orgId}:${newMemberWallet}`, { orgId, walletAddress: newMemberWallet, role: 'member' });
+
+  return NextResponse.json({ data: db.members.get(`${orgId}:${newMemberWallet}`) }, { status: 201 });
 /**
  * GET  /api/orgs/:orgId/members   — List members
  * POST /api/orgs/:orgId/members   — Add a member
diff --git a/app/lib/auth.ts b/app/lib/auth.ts
index 30edf65..be63d26 100644
--- a/app/lib/auth.ts
+++ b/app/lib/auth.ts
@@ -1,3 +1,27 @@
+import { NextResponse } from "next/server";
+import jwt from "jsonwebtoken";
+
+const JWT_SECRET = process.env.JWT_SECRET || "streampay-dev-secret-do-not-use-in-prod";
+
+export function tryAuthenticateRequest(request: Request) {
+  const authHeader = request.headers.get("authorization");
+  if (!authHeader?.startsWith("Bearer ")) {
+    return { error: "Missing or invalid authorization header" };
+  }
+  const token = authHeader.slice(7);
+  try {
+    const verified = jwt.verify(token, JWT_SECRET) as { sub?: string };
+    if (!verified.sub) {
+      return { error: "Invalid or expired token" };
+    }
+    return { walletAddress: verified.sub };
+  } catch {
+    return { error: "Invalid or expired token" };
+  }
+}
+
+export function createErrorResponse(code: string, message: string, status: number, requestId: string = "mock-request-id") {
+  return NextResponse.json({ error: { code, message, request_id: requestId } }, { status });
 /**
  * app/lib/auth.ts
  *
diff --git a/app/lib/db.ts b/app/lib/db.ts
index 0130f58..16fc16d 100644
--- a/app/lib/db.ts
+++ b/app/lib/db.ts
@@ -1,3 +1,68 @@
+import { Stream, ActivityEvent } from "@/app/types/openapi";
+import { Org, Member } from "@/app/types/org";
+
+export const db = {
+  streams: new Map<string, Stream>([
+    [
+      "stream-ada",
+      {
+        id: "stream-ada",
+        recipient: "Ada Creative Studio",
+        rate: "120 XLM / month",
+        schedule: "Pays every 30 days",
+        status: "active",
+        nextAction: "pause",
+        createdAt: "2026-04-01T09:00:00Z",
+        updatedAt: "2026-04-28T10:30:00Z",
+      },
+    ],
+    [
+      "stream-kemi",
+      {
+        id: "stream-kemi",
+        recipient: "Kemi Onboarding Support",
+        rate: "32 XLM / week",
+        schedule: "Draft stream ready to launch",
+        status: "draft",
+        nextAction: "start",
+        createdAt: "2026-04-10T14:00:00Z",
+        updatedAt: "2026-04-28T11:00:00Z",
+      },
+    ],
+    [
+      "stream-yusuf",
+      {
+        id: "stream-yusuf",
+        recipient: "Yusuf QA Partnership",
+        rate: "18 XLM / day",
+        schedule: "Ended yesterday with funds available",
+        status: "ended",
+        nextAction: "withdraw",
+        createdAt: "2026-04-15T08:00:00Z",
+        updatedAt: "2026-04-27T20:00:00Z",
+      },
+    ],
+  ]),
+
+  orgs: new Map<string, Org>([
+    ["org-1", { id: "org-1", name: "StreamPay Org", ownerWallet: "GATODH2T75IVFB7MG6ZKKIFPWFNVJBXVPUMTYV5ANT2O2ZWL7GSDZWNRW" }]
+  ]),
+
+  members: new Map<string, Member>([
+    ["org-1:GATODH2T75IVFB7MG6ZKKIFPWFNVJBXVPUMTYV5ANT2O2ZWL7GSDZWNRW", { orgId: "org-1", walletAddress: "GATODH2T75IVFB7MG6ZKKIFPWFNVJBXVPUMTYV5ANT2O2ZWL7GSDZWNRW", role: "owner" }]
+  ]),
+
+  activity: new Map<string, ActivityEvent>([
+    ["a7383234-4224-49dc-b868-0cdf37649fda", { id: "a7383234-4224-49dc-b868-0cdf37649fda", type: "wallet.connected", timestamp: "2026-04-28T09:00:00Z", description: "Wallet connected and authenticated." }],
+    ["2b9d1d0c-bef4-46bc-a783-3073b28353fc", { id: "2b9d1d0c-bef4-46bc-a783-3073b28353fc", type: "stream.created", streamId: "stream-ada", timestamp: "2026-04-01T09:00:00Z", description: "Stream 'Design Retainer' created and set to draft." }],
+    ["d1578871-4be9-4c6a-bef5-12b2b5836478", { id: "d1578871-4be9-4c6a-bef5-12b2b5836478", type: "stream.started", streamId: "stream-ada", timestamp: "2026-04-01T09:05:00Z", description: "Stream 'Design Retainer' activated." }],
+    ["288f315d-5520-46e9-8acf-96994c87b786", { id: "288f315d-5520-46e9-8acf-96994c87b786", type: "stream.created", streamId: "stream-kemi", timestamp: "2026-04-10T14:00:00Z", description: "Stream 'Kemi Onboarding Support' created as draft." }],
+    ["3bea183d-c3b5-4e96-9fbe-804f3aee49e9", { id: "3bea183d-c3b5-4e96-9fbe-804f3aee49e9", type: "stream.created", streamId: "stream-yusuf", timestamp: "2026-04-15T08:00:00Z", description: "Stream 'Yusuf QA Partnership' created." }],
+    ["5ffa85da-27a4-4f7c-bde0-e5c067a28015", { id: "5ffa85da-27a4-4f7c-bde0-e5c067a28015", type: "stream.stopped", streamId: "stream-yusuf", timestamp: "2026-04-27T20:00:00Z", description: "Stream 'Yusuf QA Partnership' stopped and settled automatically." }],
+  ]),
+
+  idempotency: new Map<string, unknown>(),
+};
 import type { ActivityEvent, ExportJob, Stream, User } from "@/app/types/openapi";
 import { createInMemoryPersistenceStore } from "@/app/lib/repositories/in-memory";
 import {
diff --git a/app/types/org.ts b/app/types/org.ts
new file mode 100644
index 0000000..9029642
--- /dev/null
+++ b/app/types/org.ts
@@ -0,0 +1,11 @@
+export interface Org {
+  id: string;
+  name: string;
+  ownerWallet: string;
+}
+
+export interface Member {
+  orgId: string;
+  walletAddress: string;
+  role: 'owner' | 'member';
+}