diff --git a/apps/api/package.json b/apps/api/package.json
index 55c1c9d..05f46ac 100644
--- a/apps/api/package.json
+++ b/apps/api/package.json
@@ -22,6 +22,8 @@
     "hono": "^4.6.17",
     "node-cron": "^3.0.3",
     "nodemailer": "^6.9.16",
+    "stripe": "^22.0.0",
+
     "zod": "^4.3.6"
   },
   "devDependencies": {
diff --git a/apps/api/src/services/payment.ts b/apps/api/src/services/payment.ts
new file mode 100644
index 0000000..ff7fcb8
--- /dev/null
+++ b/apps/api/src/services/payment.ts
@@ -0,0 +1,150 @@
+import Stripe from "stripe";
+import { getDb, clients, eq, invoices } from "@groombook/db";
+
+let _stripe: Stripe | null | undefined;
+
+function getStripeClient(): Stripe | null {
+  if (_stripe === undefined) {
+    const secretKey = process.env.STRIPE_SECRET_KEY;
+    if (!secretKey) return null;
+    _stripe = new Stripe(secretKey);
+  }
+  return _stripe;
+}
+
+export async function getOrCreateStripeCustomer(clientId: string): Promise<string | null> {
+  const stripe = getStripeClient();
+  if (!stripe) return null;
+
+  const db = getDb();
+  const [client] = await db.select().from(clients).where(eq(clients.id, clientId)).limit(1);
+  if (!client) return null;
+
+  if (client.stripeCustomerId) return client.stripeCustomerId;
+
+  const customer = await stripe.customers.create({
+    metadata: { groombook_client_id: clientId },
+  });
+
+  await db
+    .update(clients)
+    .set({ stripeCustomerId: customer.id, updatedAt: new Date() })
+    .where(eq(clients.id, clientId));
+
+  return customer.id;
+}
+
+export async function createPaymentIntent(
+  invoiceIdOrIds: string | string[],
+  clientId: string
+): Promise<{ clientSecret: string; paymentIntentId: string } | null> {
+  const stripe = getStripeClient();
+  if (!stripe) return null;
+
+  const db = getDb();
+  const invoiceIds = Array.isArray(invoiceIdOrIds) ? invoiceIdOrIds : [invoiceIdOrIds];
+
+  const invoiceRows = await db
+    .select()
+    .from(invoices)
+    .where(eq(invoices.id, invoiceIds[0]));
+
+  const [invoice] = invoiceRows;
+  if (!invoice) return null;
+
+  let totalCents = invoice.totalCents;
+  if (invoiceIds.length > 1) {
+    const allInvoices = await db
+      .select({ totalCents: invoices.totalCents })
+      .from(invoices)
+      .where(eq(invoices.id, invoiceIds[0]));
+    totalCents = allInvoices.reduce((sum, inv) => sum + inv.totalCents, totalCents);
+  }
+
+  const stripeCustomerId = await getOrCreateStripeCustomer(clientId);
+  if (!stripeCustomerId) return null;
+
+  const paymentIntent = await stripe.paymentIntents.create({
+    amount: totalCents,
+    currency: "usd",
+    customer: stripeCustomerId,
+    metadata: {
+      groombook_invoice_ids: invoiceIds.join(","),
+      groombook_client_id: clientId,
+    },
+    automatic_payment_methods: { enabled: true },
+  });
+
+  for (const invId of invoiceIds) {
+    await db
+      .update(invoices)
+      .set({ stripePaymentIntentId: paymentIntent.id, updatedAt: new Date() })
+      .where(eq(invoices.id, invId));
+  }
+
+  return {
+    clientSecret: paymentIntent.client_secret!,
+    paymentIntentId: paymentIntent.id,
+  };
+}
+
+export async function processRefund(
+  invoiceId: string,
+  amountCents?: number
+): Promise<{ refundId: string } | null> {
+  const stripe = getStripeClient();
+  if (!stripe) return null;
+
+  const db = getDb();
+  const [invoice] = await db.select().from(invoices).where(eq(invoices.id, invoiceId)).limit(1);
+  if (!invoice?.stripePaymentIntentId) return null;
+
+  const refund = await stripe.refunds.create({
+    payment_intent: invoice.stripePaymentIntentId,
+    amount: amountCents,
+  });
+
+  await db
+    .update(invoices)
+    .set({ stripeRefundId: refund.id, updatedAt: new Date() })
+    .where(eq(invoices.id, invoiceId));
+
+  return { refundId: refund.id };
+}
+
+export async function listPaymentMethods(clientId: string): Promise<Stripe.PaymentMethod[] | null> {
+  const stripe = getStripeClient();
+  if (!stripe) return null;
+
+  const stripeCustomerId = await getOrCreateStripeCustomer(clientId);
+  if (!stripeCustomerId) return null;
+
+  const methods = await stripe.paymentMethods.list({
+    customer: stripeCustomerId,
+    type: "card",
+  });
+
+  return methods.data;
+}
+
+export async function attachPaymentMethod(
+  clientId: string,
+  paymentMethodId: string
+): Promise<boolean> {
+  const stripe = getStripeClient();
+  if (!stripe) return false;
+
+  const stripeCustomerId = await getOrCreateStripeCustomer(clientId);
+  if (!stripeCustomerId) return false;
+
+  await stripe.paymentMethods.attach(paymentMethodId, { customer: stripeCustomerId });
+  return true;
+}
+
+export async function detachPaymentMethod(paymentMethodId: string): Promise<boolean> {
+  const stripe = getStripeClient();
+  if (!stripe) return false;
+
+  await stripe.paymentMethods.detach(paymentMethodId);
+  return true;
+}