diff --git a/backend/.env.example b/backend/.env.example
index d70a0f7..3e783c0 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -67,3 +67,17 @@ SILO_API_KEY=
 # value is configured on the program in Sidekick. Leave blank to disable the
 # endpoint entirely (all calls 401).
 SIDEKICK_SECRET=
+
+# Attend (https://github.com/hackclub/attend) — invites a buyer to the
+# in-person event once they purchase the ticket shop item. Event-scoped API
+# key, generated from the Attend admin UI ("regenerate API key"). Leave
+# ATTEND_API_KEY or ATTEND_EVENT_SLUG blank to disable; the feature degrades
+# silently when unconfigured.
+ATTEND_BASE_URL=https://attend.hackclub.com
+ATTEND_API_KEY=
+ATTEND_EVENT_SLUG=
+# shop_items.id of the ticket item that should trigger an Attend invite
+ATTEND_TICKET_SHOP_ITEM_ID=
+# Slack user id to DM when an invite fails after retries (an audit-log entry
+# is always written regardless; this is optional extra visibility)
+ATTEND_ALERT_SLACK_ID=
diff --git a/backend/src/attend/attend.module.ts b/backend/src/attend/attend.module.ts
new file mode 100644
index 0000000..454b1a5
--- /dev/null
+++ b/backend/src/attend/attend.module.ts
@@ -0,0 +1,8 @@
+import { Module } from '@nestjs/common';
+import { AttendService } from './attend.service';
+
+@Module({
+  providers: [AttendService],
+  exports: [AttendService],
+})
+export class AttendModule {}
diff --git a/backend/src/attend/attend.service.spec.ts b/backend/src/attend/attend.service.spec.ts
new file mode 100644
index 0000000..c0a0d8d
--- /dev/null
+++ b/backend/src/attend/attend.service.spec.ts
@@ -0,0 +1,129 @@
+import { ConfigService } from '@nestjs/config';
+import { AttendService } from './attend.service';
+import { fetchWithTimeout } from '../fetch.util';
+
+jest.mock('../fetch.util');
+
+const mockFetch = fetchWithTimeout as jest.Mock;
+
+function makeConfig(values: Record<string, string | undefined>): ConfigService {
+  return { get: (key: string) => values[key] } as unknown as ConfigService;
+}
+
+describe('AttendService', () => {
+  afterEach(() => jest.clearAllMocks());
+
+  it('is disabled and never calls fetch when unconfigured', async () => {
+    const service = new AttendService(makeConfig({}));
+    const result = await service.inviteParticipant(
+      'person@example.com',
+      'Ada Lovelace',
+    );
+    expect(result).toBe(false);
+    expect(mockFetch).not.toHaveBeenCalled();
+  });
+
+  it('posts to the configured event and splits the name', async () => {
+    mockFetch.mockResolvedValue({ ok: true, status: 201 });
+    const service = new AttendService(
+      makeConfig({
+        ATTEND_BASE_URL: 'https://attend.example.com',
+        ATTEND_API_KEY: 'secret-key',
+        ATTEND_EVENT_SLUG: 'beest',
+      }),
+    );
+
+    const result = await service.inviteParticipant(
+      'person@example.com',
+      'Ada Lovelace',
+    );
+
+    expect(result).toBe(true);
+    expect(mockFetch).toHaveBeenCalledWith(
+      'https://attend.example.com/api/v1/events/beest/participants',
+      expect.objectContaining({
+        method: 'POST',
+        headers: expect.objectContaining({
+          Authorization: 'Bearer secret-key',
+        }),
+        body: JSON.stringify({
+          email: 'person@example.com',
+          first_name: 'Ada',
+          last_name: 'Lovelace',
+        }),
+      }),
+    );
+  });
+
+  it('treats a 409 (already invited) as success', async () => {
+    mockFetch.mockResolvedValue({ ok: false, status: 409 });
+    const service = new AttendService(
+      makeConfig({
+        ATTEND_API_KEY: 'secret-key',
+        ATTEND_EVENT_SLUG: 'beest',
+      }),
+    );
+
+    const result = await service.inviteParticipant('person@example.com');
+    expect(result).toBe(true);
+  });
+
+  it('retries on HTTP error and returns false only after exhausting all attempts', async () => {
+    jest.useFakeTimers();
+    mockFetch.mockResolvedValue({ ok: false, status: 422 });
+    const service = new AttendService(
+      makeConfig({
+        ATTEND_API_KEY: 'secret-key',
+        ATTEND_EVENT_SLUG: 'beest',
+      }),
+    );
+
+    const resultPromise = service.inviteParticipant('bad-email');
+    await jest.runAllTimersAsync();
+    const result = await resultPromise;
+
+    expect(result).toBe(false);
+    expect(mockFetch).toHaveBeenCalledTimes(3);
+    jest.useRealTimers();
+  });
+
+  it('retries after a transient failure and succeeds', async () => {
+    jest.useFakeTimers();
+    mockFetch
+      .mockRejectedValueOnce(new Error('network down'))
+      .mockResolvedValueOnce({ ok: true, status: 201 });
+    const service = new AttendService(
+      makeConfig({
+        ATTEND_API_KEY: 'secret-key',
+        ATTEND_EVENT_SLUG: 'beest',
+      }),
+    );
+
+    const resultPromise = service.inviteParticipant('person@example.com');
+    await jest.runAllTimersAsync();
+    const result = await resultPromise;
+
+    expect(result).toBe(true);
+    expect(mockFetch).toHaveBeenCalledTimes(2);
+    jest.useRealTimers();
+  });
+
+  it('returns false when every attempt throws', async () => {
+    jest.useFakeTimers();
+    mockFetch.mockRejectedValue(new Error('network down'));
+    const service = new AttendService(
+      makeConfig({
+        ATTEND_API_KEY: 'secret-key',
+        ATTEND_EVENT_SLUG: 'beest',
+      }),
+    );
+
+    const resultPromise = service.inviteParticipant('person@example.com');
+    await jest.runAllTimersAsync();
+    const result = await resultPromise;
+
+    expect(result).toBe(false);
+    expect(mockFetch).toHaveBeenCalledTimes(3);
+    jest.useRealTimers();
+  });
+});
diff --git a/backend/src/attend/attend.service.ts b/backend/src/attend/attend.service.ts
new file mode 100644
index 0000000..ac7d570
--- /dev/null
+++ b/backend/src/attend/attend.service.ts
@@ -0,0 +1,95 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import { fetchWithTimeout } from '../fetch.util';
+
+/**
+ * Outbound integration with Attend (https://github.com/hackclub/attend) —
+ * invites a participant to the in-person event once they buy their ticket.
+ * Best-effort like SlackNotifyService: logs and returns false on any
+ * failure rather than throwing, so a downed Attend never blocks a purchase.
+ */
+@Injectable()
+export class AttendService {
+  private readonly logger = new Logger(AttendService.name);
+  private readonly baseUrl: string;
+  private readonly apiKey: string | undefined;
+  private readonly eventSlug: string | undefined;
+  private readonly configured: boolean;
+
+  constructor(private configService: ConfigService) {
+    this.baseUrl =
+      this.configService.get('ATTEND_BASE_URL') ??
+      'https://attend.hackclub.com';
+    this.apiKey = this.configService.get('ATTEND_API_KEY');
+    this.eventSlug = this.configService.get('ATTEND_EVENT_SLUG');
+    this.configured = !!this.apiKey && !!this.eventSlug;
+    if (!this.configured) {
+      this.logger.warn(
+        'ATTEND_API_KEY / ATTEND_EVENT_SLUG not set; Attend invites disabled',
+      );
+    }
+  }
+
+  private static readonly MAX_ATTEMPTS = 3;
+  private static readonly RETRY_DELAY_MS = 1000;
+
+  /**
+   * Invites a participant to the Attend event by email. A 409 (already
+   * invited/registered) counts as success — the goal (an invite exists)
+   * already holds. Retries transient failures (network errors, non-409
+   * non-2xx responses) up to MAX_ATTEMPTS times before giving up. Returns
+   * false only once every attempt has failed, or when unconfigured — the
+   * caller is responsible for surfacing that loudly, since a false here
+   * means a paying participant did not get invited.
+   */
+  async inviteParticipant(
+    email: string,
+    name?: string | null,
+  ): Promise<boolean> {
+    if (!this.configured) return false;
+
+    const [firstName, ...rest] = (name ?? '')
+      .trim()
+      .split(/\s+/)
+      .filter(Boolean);
+    const lastName = rest.join(' ');
+
+    let lastError = '';
+    for (let attempt = 1; attempt <= AttendService.MAX_ATTEMPTS; attempt++) {
+      try {
+        const res = await fetchWithTimeout(
+          `${this.baseUrl}/api/v1/events/${this.eventSlug}/participants`,
+          {
+            method: 'POST',
+            headers: {
+              Authorization: `Bearer ${this.apiKey}`,
+              'Content-Type': 'application/json',
+            },
+            body: JSON.stringify({
+              email,
+              ...(firstName ? { first_name: firstName } : {}),
+              ...(lastName ? { last_name: lastName } : {}),
+            }),
+          },
+        );
+
+        if (res.ok || res.status === 409) return true;
+
+        lastError = `HTTP ${res.status}`;
+      } catch (err) {
+        lastError = err instanceof Error ? err.message : String(err);
+      }
+
+      if (attempt < AttendService.MAX_ATTEMPTS) {
+        await new Promise((r) =>
+          setTimeout(r, AttendService.RETRY_DELAY_MS * attempt),
+        );
+      }
+    }
+
+    this.logger.error(
+      `Attend invite failed for ${email} after ${AttendService.MAX_ATTEMPTS} attempts: ${lastError}`,
+    );
+    return false;
+  }
+}
diff --git a/backend/src/entities/audit-log.entity.ts b/backend/src/entities/audit-log.entity.ts
index 696c804..96533a8 100644
--- a/backend/src/entities/audit-log.entity.ts
+++ b/backend/src/entities/audit-log.entity.ts
@@ -40,6 +40,7 @@ export const AUDIT_ACTIONS = [
   'admin_fulfillment_message',
   'sidekick_address_reveal',
   'sidekick_user_note_change',
+  'attend_invite_failed',
 ] as const;
 
 export type AuditAction = (typeof AUDIT_ACTIONS)[number];
diff --git a/backend/src/shop/shop.module.ts b/backend/src/shop/shop.module.ts
index eb4be06..8fa0fd4 100644
--- a/backend/src/shop/shop.module.ts
+++ b/backend/src/shop/shop.module.ts
@@ -4,6 +4,7 @@ import { AuthModule } from '../auth/auth.module';
 import { AuditLogModule } from '../audit-log/audit-log.module';
 import { RsvpModule } from '../rsvp/rsvp.module';
 import { SlackModule } from '../slack/slack.module';
+import { AttendModule } from '../attend/attend.module';
 import { ShopItem } from '../entities/shop-item.entity';
 import { Order } from '../entities/order.entity';
 import { FulfillmentUpdate } from '../entities/fulfillment-update.entity';
@@ -20,6 +21,7 @@ import { ShopService } from './shop.service';
     AuditLogModule,
     RsvpModule,
     SlackModule,
+    AttendModule,
   ],
   controllers: [ShopController],
   providers: [ShopService],
diff --git a/backend/src/shop/shop.service.ts b/backend/src/shop/shop.service.ts
index 1e63d15..419a7ef 100644
--- a/backend/src/shop/shop.service.ts
+++ b/backend/src/shop/shop.service.ts
@@ -7,6 +7,7 @@ import {
   Logger,
 } from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
+import { ConfigService } from '@nestjs/config';
 import { Repository, DataSource, In } from 'typeorm';
 import { ShopItem } from '../entities/shop-item.entity';
 import { Project } from '../entities/project.entity';
@@ -18,6 +19,7 @@ import { ShopSuggestionVote } from '../entities/shop-suggestion-vote.entity';
 import { AuditLogService } from '../audit-log/audit-log.service';
 import { RsvpService } from '../rsvp/rsvp.service';
 import { SlackNotifyService } from '../slack/slack-notify.service';
+import { AttendService } from '../attend/attend.service';
 import {
   orderPendingDm,
   orderFulfilledDm,
@@ -59,6 +61,8 @@ export class ShopService {
     private readonly auditLogService: AuditLogService,
     private readonly rsvpService: RsvpService,
     private readonly slackNotify: SlackNotifyService,
+    private readonly attendService: AttendService,
+    private readonly configService: ConfigService,
   ) {}
 
   /** Fire-and-forget order-status DM to the buyer (best-effort). */
@@ -76,6 +80,31 @@ export class ShopService {
       .catch(() => undefined);
   }
 
+  /**
+   * Surfaces an Attend invite failure loudly: an audit-log entry (searchable
+   * in the admin UI against the buyer) plus, if ATTEND_ALERT_SLACK_ID is set,
+   * a direct Slack DM so someone actually sees it instead of it sitting in a
+   * log file.
+   */
+  private async alertAttendInviteFailure(
+    userId: string,
+    email: string,
+  ): Promise<void> {
+    await this.auditLogService.log(
+      userId,
+      'attend_invite_failed',
+      `Attend invite failed for ${email} — needs manual follow-up`,
+    );
+
+    const alertSlackId = this.configService.get<string>('ATTEND_ALERT_SLACK_ID');
+    if (alertSlackId) {
+      await this.slackNotify.dm(
+        alertSlackId,
+        `Attend invite failed for ${email} after retries — they bought a ticket but weren't invited. Needs manual invite.`,
+      );
+    }
+  }
+
   // ── Shop suggestions ──
 
   async listSuggestions(userId: string) {
@@ -343,6 +372,23 @@ export class ShopService {
         if (u?.email) this.rsvpService.updateDateField(u.email, 'Loops - beestPurchasedItem');
       });
 
+      // Ticket item purchased — invite the buyer to the in-person event on Attend.
+      // A failed invite means a paying participant won't get into the event, so
+      // failures (after AttendService's own retries) must be surfaced loudly:
+      // an audit-log entry (visible/searchable in the admin UI) plus a direct
+      // Slack DM, rather than just a swallowed log line.
+      const ticketItemId = this.configService.get<string>('ATTEND_TICKET_SHOP_ITEM_ID');
+      if (ticketItemId && shopItemId === ticketItemId) {
+        this.userRepo
+          .findOne({ where: { id: userId }, select: ['email', 'name'] })
+          .then(async (u) => {
+            if (!u?.email) return;
+            const invited = await this.attendService.inviteParticipant(u.email, u.name);
+            if (!invited) await this.alertAttendInviteFailure(userId, u.email);
+          })
+          .catch(() => undefined);
+      }
+
       this.notifyOrder(
         userId,
         orderPendingDm({