diff --git a/apps/booking/nuxt.config.ts b/apps/booking/nuxt.config.ts
index 1519add..04ceea5 100644
--- a/apps/booking/nuxt.config.ts
+++ b/apps/booking/nuxt.config.ts
@@ -18,6 +18,10 @@ export default defineNuxtConfig({
     public: {
       siteUrl: process.env.NUXT_PUBLIC_SITE_URL
         || (process.env.NODE_ENV === 'production' ? 'https://booking.dezky.eu' : 'http://localhost:3000'),
+      // Cloudflare Turnstile site-key. When set, the booking form renders a
+      // captcha widget and sends its token with the booking POST. Server-side
+      // enforcement is gated independently by TURNSTILE_SECRET on platform-api.
+      turnstileSiteKey: process.env.NUXT_PUBLIC_TURNSTILE_SITE_KEY || '',
     },
   },
 
diff --git a/apps/booking/pages/[tenantSlug]/[hostSlug]/[eventTypeSlug].vue b/apps/booking/pages/[tenantSlug]/[hostSlug]/[eventTypeSlug].vue
index aafd9c5..ac1311e 100644
--- a/apps/booking/pages/[tenantSlug]/[hostSlug]/[eventTypeSlug].vue
+++ b/apps/booking/pages/[tenantSlug]/[hostSlug]/[eventTypeSlug].vue
@@ -30,6 +30,71 @@ const submitting = ref(false)
 const submitError = ref<string | null>(null)
 const booking = ref<PublicBooking | null>(null)
 
+// Cloudflare Turnstile (optional). Only when a public site-key is configured do
+// we load the script + render a widget on the details step; otherwise the form
+// behaves exactly as before. We never solve the captcha — the widget produces a
+// token that we forward to platform-api, which verifies it server-side.
+const turnstileSiteKey = useRuntimeConfig().public.turnstileSiteKey as string
+const captchaToken = ref<string | null>(null)
+const captchaEl = ref<HTMLElement | null>(null)
+let captchaWidgetId: string | null = null
+const TURNSTILE_SRC = 'https://challenges.cloudflare.com/turnstile/v0/api.js'
+
+function loadTurnstileScript(): Promise<void> {
+  return new Promise((resolve, reject) => {
+    if ((window as any).turnstile) return resolve()
+    const existing = document.querySelector(`script[src^="${TURNSTILE_SRC}"]`) as HTMLScriptElement | null
+    if (existing) {
+      existing.addEventListener('load', () => resolve())
+      existing.addEventListener('error', () => reject(new Error('turnstile load failed')))
+      return
+    }
+    const s = document.createElement('script')
+    s.src = TURNSTILE_SRC
+    s.async = true
+    s.defer = true
+    s.addEventListener('load', () => resolve())
+    s.addEventListener('error', () => reject(new Error('turnstile load failed')))
+    document.head.appendChild(s)
+  })
+}
+
+async function renderCaptcha() {
+  if (!turnstileSiteKey || !import.meta.client || !captchaEl.value || captchaWidgetId) return
+  try {
+    await loadTurnstileScript()
+    const turnstile = (window as any).turnstile
+    if (!turnstile || !captchaEl.value) return
+    captchaWidgetId = turnstile.render(captchaEl.value, {
+      sitekey: turnstileSiteKey,
+      callback: (token: string) => {
+        captchaToken.value = token
+      },
+      'expired-callback': () => {
+        captchaToken.value = null
+      },
+      'error-callback': () => {
+        captchaToken.value = null
+      },
+    })
+  } catch {
+    // If the widget can't load we leave captchaToken null; the server decides
+    // whether that's fatal (it is only when TURNSTILE_SECRET is set).
+  }
+}
+
+function resetCaptcha() {
+  captchaToken.value = null
+  if (import.meta.client && captchaWidgetId && (window as any).turnstile) {
+    ;(window as any).turnstile.reset(captchaWidgetId)
+  }
+}
+
+// Render the widget whenever the details step becomes visible.
+watch(step, (s) => {
+  if (s === 'details' && turnstileSiteKey) void nextTick(renderCaptcha)
+})
+
 // Whitelabel theming — drive the accent from the tenant's brandColor.
 watchEffect(() => {
   if (!import.meta.client || !info.value) return
@@ -90,6 +155,7 @@ async function confirm() {
           attendeeEmail: form.email,
           attendeeTimezone: visitorTz.value,
           attendeeNotes: form.notes || undefined,
+          captchaToken: captchaToken.value || undefined,
         },
       })
     }
@@ -101,6 +167,9 @@ async function confirm() {
       await loadSlots()
     } else if (e?.statusCode === 503) {
       submitError.value = 'The calendar is temporarily unavailable. Please try again in a moment.'
+    } else if (e?.statusCode === 403) {
+      submitError.value = 'Captcha verification failed. Please complete the challenge and try again.'
+      resetCaptcha()
     } else {
       submitError.value = e?.statusMessage || 'Something went wrong. Please try again.'
     }
@@ -222,8 +291,13 @@ useHead(() => ({ title: info.value ? `${info.value.eventType.title} · ${info.va
             <label class="bk-label" for="notes">Notes (optional)</label>
             <textarea id="notes" v-model="form.notes" class="bk-input" maxlength="2000" />
           </div>
+          <div v-if="turnstileSiteKey" ref="captchaEl" class="captcha" />
           <p v-if="submitError" class="err">{{ submitError }}</p>
-          <button type="submit" class="bk-btn bk-btn--primary" :disabled="submitting">
+          <button
+            type="submit"
+            class="bk-btn bk-btn--primary"
+            :disabled="submitting || (!!turnstileSiteKey && !captchaToken)"
+          >
             {{ submitting ? 'Confirming…' : 'Confirm booking' }}
           </button>
         </form>
@@ -271,6 +345,7 @@ useHead(() => ({ title: info.value ? `${info.value.eventType.title} · ${info.va
 .slot { height: 44px; border: 1px solid var(--border); border-radius: 10px; background: var(--surface); font-size: 15px; font-weight: 600; cursor: pointer; }
 .slot:hover { border-color: var(--accent); }
 .form { display: flex; flex-direction: column; gap: 16px; margin-top: 14px; }
+.captcha { min-height: 65px; }
 .chosen { font-weight: 600; margin: 0 0 6px; }
 .back { background: none; border: none; color: var(--text-mute); cursor: pointer; padding: 0 0 12px; font-size: 14px; }
 .done { text-align: center; }
diff --git a/infrastructure/docker-compose/docker-compose.yml b/infrastructure/docker-compose/docker-compose.yml
index 5d4dbb7..c69eb03 100644
--- a/infrastructure/docker-compose/docker-compose.yml
+++ b/infrastructure/docker-compose/docker-compose.yml
@@ -590,6 +590,9 @@ services:
       DEZKY_TRAEFIK: "1"
       # How nitro reaches platform-api inside the docker network.
       PLATFORM_API_INTERNAL_URL: http://platform-api:3001
+      # Optional Cloudflare Turnstile site-key — when set, the booking form
+      # renders a captcha widget. Empty by default (no widget).
+      NUXT_PUBLIC_TURNSTILE_SITE_KEY: ${NUXT_PUBLIC_TURNSTILE_SITE_KEY:-}
     volumes:
       - ../../apps/booking:/app
       - booking_node_modules:/app/node_modules
@@ -686,6 +689,9 @@ services:
       SCHEDULING_CREDENTIAL_KEY: ${SCHEDULING_CREDENTIAL_KEY}
       BOOKING_PUBLIC_URL: ${BOOKING_PUBLIC_URL:-https://booking.dezky.local}
       MEET_PUBLIC_URL: ${MEET_PUBLIC_URL:-https://meet.dezky.local}
+      # Optional Cloudflare Turnstile secret. When set, the public booking holds
+      # and bookings endpoints verify the visitor's captcha token; unset = no-op.
+      TURNSTILE_SECRET: ${TURNSTILE_SECRET:-}
     volumes:
       - ../../services/platform-api:/app
       - platform_api_node_modules:/app/node_modules
diff --git a/services/platform-api/src/scheduling/abuse/abuse-guard.ts b/services/platform-api/src/scheduling/abuse/abuse-guard.ts
new file mode 100644
index 0000000..befc5da
--- /dev/null
+++ b/services/platform-api/src/scheduling/abuse/abuse-guard.ts
@@ -0,0 +1,85 @@
+import { ForbiddenException, Injectable, Logger } from '@nestjs/common'
+import { ConfigService } from '@nestjs/config'
+
+// Pluggable abuse guard for the public booking surface (spec §6.1). The default
+// is a no-op so unconfigured environments behave exactly as before. When a
+// captcha provider is configured (currently Cloudflare Turnstile via
+// TURNSTILE_SECRET) the guard verifies the visitor-supplied token and rejects
+// requests it can't validate. We deliberately do NOT solve captchas — we only
+// forward the token the browser widget produced to the provider's siteverify.
+
+export const ABUSE_GUARD = Symbol('ABUSE_GUARD')
+
+export interface AbuseGuard {
+  // Whether a captcha token is expected from the client. The booking app uses
+  // this to decide whether to render a widget (mirrored client-side via the
+  // public site-key env), but the server is the source of truth on enforcement.
+  readonly enabled: boolean
+
+  // Verify a request. `token` is the captcha token from the client, if any.
+  // `remoteIp` is the visitor IP for providers that score on it. Throws a 4xx
+  // when the token is missing/invalid; resolves silently when acceptable.
+  verify(token: string | undefined, remoteIp?: string): Promise<void>
+}
+
+// No-op guard — accepts everything. Used when no captcha provider is configured.
+@Injectable()
+export class NoopAbuseGuard implements AbuseGuard {
+  readonly enabled = false
+
+  async verify(): Promise<void> {
+    // Intentionally does nothing.
+  }
+}
+
+interface TurnstileVerifyResponse {
+  success: boolean
+  'error-codes'?: string[]
+}
+
+// Cloudflare Turnstile verifier. Posts the client token to siteverify with the
+// secret; any non-success (missing token, network error, provider rejection)
+// becomes a 403 so we fail closed once captcha is switched on.
+@Injectable()
+export class TurnstileAbuseGuard implements AbuseGuard {
+  readonly enabled = true
+  private readonly logger = new Logger(TurnstileAbuseGuard.name)
+  private static readonly SITEVERIFY = 'https://challenges.cloudflare.com/turnstile/v0/siteverify'
+
+  constructor(private readonly secret: string) {}
+
+  async verify(token: string | undefined, remoteIp?: string): Promise<void> {
+    if (!token) throw new ForbiddenException('Captcha verification required.')
+
+    const form = new URLSearchParams()
+    form.set('secret', this.secret)
+    form.set('response', token)
+    if (remoteIp) form.set('remoteip', remoteIp)
+
+    let body: TurnstileVerifyResponse
+    try {
+      const res = await fetch(TurnstileAbuseGuard.SITEVERIFY, {
+        method: 'POST',
+        headers: { 'content-type': 'application/x-www-form-urlencoded' },
+        body: form,
+      })
+      body = (await res.json()) as TurnstileVerifyResponse
+    } catch (err) {
+      // Fail closed: if we can't reach the verifier we don't let the request through.
+      this.logger.error(`Turnstile siteverify request failed: ${String(err)}`)
+      throw new ForbiddenException('Captcha verification unavailable. Please try again.')
+    }
+
+    if (!body.success) {
+      this.logger.warn(`Turnstile rejected token: ${(body['error-codes'] ?? []).join(', ') || 'unknown'}`)
+      throw new ForbiddenException('Captcha verification failed.')
+    }
+  }
+}
+
+// Factory used by the module: pick Turnstile when its secret is set, else no-op.
+export function abuseGuardFactory(config: ConfigService): AbuseGuard {
+  const secret = config.get<string>('TURNSTILE_SECRET')?.trim()
+  if (secret) return new TurnstileAbuseGuard(secret)
+  return new NoopAbuseGuard()
+}
diff --git a/services/platform-api/src/scheduling/public/dto/public-dtos.ts b/services/platform-api/src/scheduling/public/dto/public-dtos.ts
index 432e697..cd55aca 100644
--- a/services/platform-api/src/scheduling/public/dto/public-dtos.ts
+++ b/services/platform-api/src/scheduling/public/dto/public-dtos.ts
@@ -20,6 +20,13 @@ export class SlotsQueryDto {
 export class CreateHoldDto {
   @IsISO8601()
   startUtc!: string
+
+  // Optional captcha token (e.g. Cloudflare Turnstile). Enforced server-side
+  // only when a captcha provider is configured; ignored otherwise.
+  @IsOptional()
+  @IsString()
+  @MaxLength(4096)
+  captchaToken?: string
 }
 
 export class CreateBookingDto {
@@ -48,6 +55,13 @@ export class CreateBookingDto {
   @IsString()
   @MaxLength(64)
   holdId?: string
+
+  // Optional captcha token (e.g. Cloudflare Turnstile). Enforced server-side
+  // only when a captcha provider is configured; ignored otherwise.
+  @IsOptional()
+  @IsString()
+  @MaxLength(4096)
+  captchaToken?: string
 }
 
 export class CancelBookingDto {
diff --git a/services/platform-api/src/scheduling/public/public-scheduling.controller.ts b/services/platform-api/src/scheduling/public/public-scheduling.controller.ts
index 1e6a095..d1b3224 100644
--- a/services/platform-api/src/scheduling/public/public-scheduling.controller.ts
+++ b/services/platform-api/src/scheduling/public/public-scheduling.controller.ts
@@ -1,6 +1,7 @@
-import { Body, Controller, Get, Param, Post, Query, UseGuards } from '@nestjs/common'
+import { Body, Controller, Get, Inject, Ip, Param, Post, Query, UseGuards } from '@nestjs/common'
 import { Throttle, ThrottlerGuard } from '@nestjs/throttler'
 import { TenantsService } from '../../tenants/tenants.service.js'
+import { ABUSE_GUARD, type AbuseGuard } from '../abuse/abuse-guard.js'
 import type { BookingContext } from '../bookings/bookings.service.js'
 import { BookingsService } from '../bookings/bookings.service.js'
 import { EventTypesService } from '../event-types/event-types.service.js'
@@ -29,6 +30,7 @@ export class PublicSchedulingController {
     private readonly tenants: TenantsService,
     private readonly hosts: HostsService,
     private readonly eventTypes: EventTypesService,
+    @Inject(ABUSE_GUARD) private readonly abuseGuard: AbuseGuard,
   ) {}
 
   @Get(':tenantSlug/:hostSlug/:eventTypeSlug')
@@ -65,7 +67,9 @@ export class PublicSchedulingController {
     @Param('hostSlug') hostSlug: string,
     @Param('eventTypeSlug') eventTypeSlug: string,
     @Body() dto: CreateHoldDto,
+    @Ip() ip: string,
   ) {
+    await this.abuseGuard.verify(dto.captchaToken, ip)
     const ctx = await this.publicSvc.resolveContext(tenantSlug, hostSlug, eventTypeSlug)
     const { holdId, expiresAt } = await this.bookings.hold(ctx, new Date(dto.startUtc))
     return { holdId, expiresAt: expiresAt.toISOString() }
@@ -78,7 +82,9 @@ export class PublicSchedulingController {
     @Param('hostSlug') hostSlug: string,
     @Param('eventTypeSlug') eventTypeSlug: string,
     @Body() dto: CreateBookingDto,
+    @Ip() ip: string,
   ) {
+    await this.abuseGuard.verify(dto.captchaToken, ip)
     const ctx = await this.publicSvc.resolveContext(tenantSlug, hostSlug, eventTypeSlug)
     const booking = await this.bookings.confirm(ctx, {
       startUtc: new Date(dto.startUtc),
diff --git a/services/platform-api/src/scheduling/scheduling.module.ts b/services/platform-api/src/scheduling/scheduling.module.ts
index e459ccc..0a7b8b0 100644
--- a/services/platform-api/src/scheduling/scheduling.module.ts
+++ b/services/platform-api/src/scheduling/scheduling.module.ts
@@ -1,4 +1,5 @@
 import { Module } from '@nestjs/common'
+import { ConfigService } from '@nestjs/config'
 import { MongooseModule } from '@nestjs/mongoose'
 import { ScheduleModule } from '@nestjs/schedule'
 import { ThrottlerModule } from '@nestjs/throttler'
@@ -12,6 +13,7 @@ import { SlotLock, SlotLockSchema } from '../schemas/slot-lock.schema.js'
 import { Tenant, TenantSchema } from '../schemas/tenant.schema.js'
 import { User, UserSchema } from '../schemas/user.schema.js'
 import { TenantsModule } from '../tenants/tenants.module.js'
+import { ABUSE_GUARD, abuseGuardFactory } from './abuse/abuse-guard.js'
 import { AvailabilityService } from './availability/availability.service.js'
 import { BookingsService } from './bookings/bookings.service.js'
 import { CalendarRetryWorker } from './bookings/calendar-retry.worker.js'
@@ -61,6 +63,9 @@ import { StalwartCalendarModule } from './stalwart-calendar/stalwart-calendar.mo
     JmapMailer,
     BookingReminderWorker,
     CalendarRetryWorker,
+    // Pluggable captcha guard for the public booking surface (Turnstile when
+    // TURNSTILE_SECRET is set, otherwise a no-op).
+    { provide: ABUSE_GUARD, useFactory: abuseGuardFactory, inject: [ConfigService] },
   ],
 })
 export class SchedulingModule {}