diff --git a/backend/config.py b/backend/config.py
index f5af700..fe4c7be 100644
--- a/backend/config.py
+++ b/backend/config.py
@@ -30,3 +30,4 @@ CLAUDE_CLI = "claude"
 MODEL_GUIDE = "claude-opus-4-8"
 MODEL_BAUSTEIN_GEN = "claude-sonnet-4-6"
 MODEL_BAUSTEIN_REWORK = "claude-sonnet-4-6"
+MODEL_CHAT = "claude-sonnet-4-6"
diff --git a/backend/generator.py b/backend/generator.py
index 42fb82a..9a04ed1 100644
--- a/backend/generator.py
+++ b/backend/generator.py
@@ -16,6 +16,7 @@ from config import (
     MODEL_GUIDE,
     MODEL_BAUSTEIN_GEN,
     MODEL_BAUSTEIN_REWORK,
+    MODEL_CHAT,
     STORAGE_DIR,
 )
 from database import (
@@ -556,6 +557,48 @@ def _build_topic_suggest_prompt(problem: str, existing_topics: list[str]) -> str
     return template.replace("{problem}", problem).replace("{existing}", existing)
 
 
+def _build_guide_chat_prompt(topic: str, format_name: str, section: str, outline: str, messages: list[dict]) -> str:
+    transcript = "\n".join(
+        f"{'Nutzer' if m.get('role') == 'user' else 'Assistent'}: {m.get('content', '')}"
+        for m in messages
+    )
+    outline_block = outline.strip() or "(keine)"
+    section_block = section.strip() or "(kein Abschnitt erkannt)"
+    return f"""Du bist ein hilfreicher Tutor zum Lern-Guide "{topic}" (Format: {format_name}). Ein Leser stellt dir Fragen, während er den Guide liest.
+
+GLIEDERUNG DES GUIDES:
+{outline_block}
+
+AKTUELLER ABSCHNITT, DEN DER LESER GERADE LIEST:
+{section_block}
+
+BISHERIGER CHAT-VERLAUF:
+{transcript}
+
+Antworte als Assistent auf die letzte Nutzer-Nachricht.
+
+WICHTIG – Antwortstil:
+- KURZ und EINFACH: 1–3 Sätze, klare Sprache.
+- Keine Einleitung, keine Wiederholung der Frage, kein Markdown-Drumherum.
+- Beantworte nur die Frage; nutze den Abschnitt und die Gliederung als Kontext.
+
+Gib NUR die Antwort aus, kein Präfix wie "Assistent:"."""
+
+
+async def chat_with_guide(topic: str, format_name: str, section: str, outline: str, messages: list[dict]) -> str:
+    try:
+        prompt = _build_guide_chat_prompt(topic, format_name, section, outline, messages)
+        returncode, stdout, stderr = await _run_claude(
+            "chat-" + str(uuid.uuid4()), prompt, 120, tools=None, model=MODEL_CHAT
+        )
+        if returncode != 0:
+            return "Entschuldigung, das hat nicht geklappt. Bitte versuche es erneut."
+        reply = stdout.strip()
+        return reply or "Entschuldigung, ich habe keine Antwort erhalten."
+    except Exception:
+        return "Entschuldigung, das hat nicht geklappt. Bitte versuche es erneut."
+
+
 async def suggest_topics(problem: str, existing_topics: list[str] | None = None) -> list[dict]:
     try:
         prompt = _build_topic_suggest_prompt(problem, existing_topics or [])
diff --git a/backend/models.py b/backend/models.py
index 95bfab6..6b79d3a 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -75,3 +75,18 @@ class TopicSuggestRequest(BaseModel):
 class TopicSuggestion(BaseModel):
     title: str
     reason: str
+
+
+class ChatMessage(BaseModel):
+    role: Literal["user", "assistant"]
+    content: str = Field(min_length=1, max_length=8000)
+
+
+class GuideChatRequest(BaseModel):
+    section: str = Field(default="", max_length=20000)
+    outline: str = Field(default="", max_length=8000)
+    messages: list[ChatMessage] = Field(min_length=1)
+
+
+class GuideChatResponse(BaseModel):
+    reply: str
diff --git a/backend/routes.py b/backend/routes.py
index 08bb6de..e37878f 100644
--- a/backend/routes.py
+++ b/backend/routes.py
@@ -11,11 +11,12 @@ from database import (
     create_baustein as db_create_baustein, list_bausteine, get_baustein, delete_baustein as db_delete_baustein,
     list_suggestions, get_suggestion, update_suggestion, delete_suggestion,
 )
-from generator import generate_guide, rework_guide, cancel_guide, generate_suggestions, generate_baustein_detail, rework_baustein, sort_bausteine, suggest_topics, is_suggestions_generating, is_sorting
+from generator import generate_guide, rework_guide, cancel_guide, generate_suggestions, generate_baustein_detail, rework_baustein, sort_bausteine, suggest_topics, chat_with_guide, is_suggestions_generating, is_sorting
 from models import (
     GuideCreateRequest, GuideReworkRequest, GuideResponse,
     BausteinCreateRequest, BausteinReworkRequest, BausteinSortRequest, BausteinResponse, SuggestionResponse,
     TopicSuggestRequest, TopicSuggestion,
+    GuideChatRequest, GuideChatResponse,
 )
 from paths import final_paths
 
@@ -89,6 +90,18 @@ async def rework(guide_id: str, req: GuideReworkRequest):
     return {"ok": True}
 
 
+@router.post("/guides/{guide_id}/chat", response_model=GuideChatResponse)
+async def guide_chat(guide_id: str, req: GuideChatRequest):
+    guide = await get_guide(guide_id)
+    if guide is None:
+        raise HTTPException(404, "Guide nicht gefunden")
+    reply = await chat_with_guide(
+        guide["topic"], guide["format"], req.section, req.outline,
+        [m.model_dump() for m in req.messages],
+    )
+    return {"reply": reply}
+
+
 @router.post("/guides/{guide_id}/cancel")
 async def cancel(guide_id: str):
     cancelled = await cancel_guide(guide_id)
diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index 26820c2..15b48b7 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -8,6 +8,8 @@
       "name": "frontend",
       "version": "0.0.0",
       "dependencies": {
+        "dompurify": "^3.4.7",
+        "marked": "^18.0.4",
         "vue": "^3.5.32"
       },
       "devDependencies": {
@@ -868,6 +870,13 @@
         "tslib": "^2.4.0"
       }
     },
+    "node_modules/@types/trusted-types": {
+      "version": "2.0.7",
+      "resolved": "https://registry.npmjs.org/@types/trusted-types/-/trusted-types-2.0.7.tgz",
+      "integrity": "sha512-ScaPdn1dQczgbl0QFTeTOmVHFULt394XJgOQNoyVhZ6r2vLnMLJfBPd53SB52T/3G36VI1/g2MZaX0cwDuXsfw==",
+      "license": "MIT",
+      "optional": true
+    },
     "node_modules/@vitejs/plugin-vue": {
       "version": "6.0.7",
       "resolved": "https://registry.npmjs.org/@vitejs/plugin-vue/-/plugin-vue-6.0.7.tgz",
@@ -1260,6 +1269,15 @@
         "node": ">=8"
       }
     },
+    "node_modules/dompurify": {
+      "version": "3.4.7",
+      "resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.4.7.tgz",
+      "integrity": "sha512-2jBxDJY4RR06tQNy4w5FlFH7kfxsQZlufd0sbv+chfHCxeJwrFw2baUDsSwvBISD4K4RDbd0PTfy3uNXsR6siA==",
+      "license": "(MPL-2.0 OR Apache-2.0)",
+      "optionalDependencies": {
+        "@types/trusted-types": "^2.0.7"
+      }
+    },
     "node_modules/electron-to-chromium": {
       "version": "1.5.361",
       "resolved": "https://registry.npmjs.org/electron-to-chromium/-/electron-to-chromium-1.5.361.tgz",
@@ -1726,6 +1744,18 @@
         "@jridgewell/sourcemap-codec": "^1.5.5"
       }
     },
+    "node_modules/marked": {
+      "version": "18.0.4",
+      "resolved": "https://registry.npmjs.org/marked/-/marked-18.0.4.tgz",
+      "integrity": "sha512-c/BTaKzg0G6ezQx97DAkYU7k0HM6ys0FqYeKBL6hlBByZwy+ycA1+f0vDdjMHKKeEjdgkx0GOv9Il6D+85cOqA==",
+      "license": "MIT",
+      "bin": {
+        "marked": "bin/marked.js"
+      },
+      "engines": {
+        "node": ">= 20"
+      }
+    },
     "node_modules/mrmime": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/mrmime/-/mrmime-2.0.1.tgz",
diff --git a/frontend/package.json b/frontend/package.json
index ed0a264..7a89248 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -9,6 +9,8 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "dompurify": "^3.4.7",
+    "marked": "^18.0.4",
     "vue": "^3.5.32"
   },
   "devDependencies": {
diff --git a/frontend/src/api.js b/frontend/src/api.js
index a811a02..a033adf 100644
--- a/frontend/src/api.js
+++ b/frontend/src/api.js
@@ -44,6 +44,15 @@ export function htmlUrl(id) {
   return `${BASE}/guides/${id}/html`
 }
 
+export async function chatGuide(id, { section, outline, messages }) {
+  const res = await fetch(`${BASE}/guides/${id}/chat`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ section, outline, messages }),
+  })
+  return res.json()
+}
+
 export async function suggestTopics(problem) {
   const res = await fetch(`${BASE}/topic-suggestions`, {
     method: 'POST',
diff --git a/frontend/src/components/TopicDetail.vue b/frontend/src/components/TopicDetail.vue
index 6351d07..37fb1f1 100644
--- a/frontend/src/components/TopicDetail.vue
+++ b/frontend/src/components/TopicDetail.vue
@@ -1,6 +1,14 @@
 <script setup>
-import { computed } from 'vue'
-import { htmlUrl } from '../api.js'
+import { computed, ref, nextTick } from 'vue'
+import { marked } from 'marked'
+import DOMPurify from 'dompurify'
+import { htmlUrl, chatGuide } from '../api.js'
+
+marked.setOptions({ breaks: true, gfm: true })
+
+function renderMarkdown(text) {
+  return DOMPurify.sanitize(marked.parse(text || ''))
+}
 
 const props = defineProps({
   previewGuide: { type: Object, default: null },
@@ -9,25 +17,142 @@ const props = defineProps({
 const LANDSCAPE_FORMATS = ['OnePager', 'Cheatsheet']
 const isLandscape = computed(() => LANDSCAPE_FORMATS.includes(props.previewGuide?.format))
 
+const frameEl = ref(null)
+
 function injectPadding(e) {
   if (isLandscape.value) return
   const doc = e.target.contentDocument
   if (!doc) return
   const style = doc.createElement('style')
-  style.textContent = '@media screen { body { padding: 2.5rem 3rem; } }'
+  style.textContent = `@media screen {
+    html { background: #f0f1f4; }
+    body {
+      zoom: 1.15;
+      max-width: 1000px;
+      margin: 0 auto;
+      padding: 2.5rem 3.5rem;
+      background: #fff;
+      box-shadow: 0 1px 8px rgba(0, 0, 0, 0.08);
+    }
+  }`
   doc.head?.appendChild(style)
 }
+
+// --- Chat ---
+const chatOpen = ref(false)
+const messages = ref([])
+const input = ref('')
+const loading = ref(false)
+const messagesEl = ref(null)
+const inputEl = ref(null)
+
+function openChat() {
+  chatOpen.value = true
+}
+
+function closeChat() {
+  chatOpen.value = false
+  messages.value = []
+  input.value = ''
+}
+
+function extractContext() {
+  try {
+    const doc = frameEl.value?.contentDocument
+    if (!doc) return { section: '', outline: '' }
+    const headings = Array.from(doc.querySelectorAll('h1, h2, h3'))
+    if (!headings.length) return { section: '', outline: '' }
+
+    const outline = headings.map((h) => h.innerText.trim()).filter(Boolean).join('\n')
+
+    // Aktuelle Überschrift = letzte, die oben im sichtbaren Bereich oder darüber liegt
+    let current = headings[0]
+    for (const h of headings) {
+      if (h.getBoundingClientRect().top <= 100) current = h
+      else break
+    }
+    const level = Number(current.tagName[1])
+    const idx = headings.indexOf(current)
+    let end = null
+    for (let i = idx + 1; i < headings.length; i++) {
+      if (Number(headings[i].tagName[1]) <= level) { end = headings[i]; break }
+    }
+    const range = doc.createRange()
+    range.setStartBefore(current)
+    if (end) range.setEndBefore(end)
+    else range.setEndAfter(doc.body.lastElementChild || doc.body)
+    const section = range.toString().trim().slice(0, 18000)
+    return { section, outline: outline.slice(0, 7000) }
+  } catch {
+    return { section: '', outline: '' }
+  }
+}
+
+async function scrollToBottom() {
+  await nextTick()
+  if (messagesEl.value) messagesEl.value.scrollTop = messagesEl.value.scrollHeight
+}
+
+async function send() {
+  const text = input.value.trim()
+  if (!text || loading.value || !props.previewGuide) return
+  messages.value.push({ role: 'user', content: text })
+  input.value = ''
+  loading.value = true
+  scrollToBottom()
+  try {
+    const { section, outline } = extractContext()
+    const res = await chatGuide(props.previewGuide.id, {
+      section,
+      outline,
+      messages: messages.value,
+    })
+    messages.value.push({ role: 'assistant', content: res.reply || '…' })
+  } catch {
+    messages.value.push({ role: 'assistant', content: 'Fehler bei der Anfrage.' })
+  } finally {
+    loading.value = false
+    scrollToBottom()
+    nextTick(() => inputEl.value?.focus())
+  }
+}
 </script>
 
 <template>
   <div class="detail">
-    <div class="preview" v-if="previewGuide">
-      <iframe :src="htmlUrl(previewGuide.id)" class="preview-frame" :class="{ landscape: isLandscape }" title="Guide-Vorschau" @load="injectPadding"></iframe>
+    <div class="preview" :class="{ landscape: isLandscape }" v-if="previewGuide">
+      <iframe ref="frameEl" :src="htmlUrl(previewGuide.id)" class="preview-frame" :class="{ landscape: isLandscape }" title="Guide-Vorschau" @load="injectPadding"></iframe>
     </div>
 
     <div class="empty-preview" v-else>
       <p>Guide-Format anklicken um zu generieren oder Vorschau zu öffnen.</p>
     </div>
+
+    <button v-if="previewGuide && !chatOpen" class="chat-fab" title="Fragen zum Guide" @click="openChat">💬</button>
+
+    <div v-if="previewGuide && chatOpen" class="chat-panel">
+      <header class="chat-header">
+        <span>Fragen zum Guide</span>
+        <button class="chat-close" title="Chat beenden" @click="closeChat">×</button>
+      </header>
+      <div ref="messagesEl" class="chat-messages">
+        <p v-if="!messages.length" class="chat-hint">Stell eine Frage zum aktuellen Abschnitt.</p>
+        <template v-for="(m, i) in messages" :key="i">
+          <div v-if="m.role === 'assistant'" class="chat-msg assistant markdown" v-html="renderMarkdown(m.content)"></div>
+          <div v-else class="chat-msg user">{{ m.content }}</div>
+        </template>
+        <div v-if="loading" class="chat-msg assistant chat-typing">Denkt…</div>
+      </div>
+      <div class="chat-input">
+        <textarea
+          ref="inputEl"
+          v-model="input"
+          placeholder="Frage stellen…"
+          @keydown.enter.exact.prevent="send"
+        ></textarea>
+        <button :disabled="!input.trim() || loading" @click="send">➤</button>
+      </div>
+    </div>
   </div>
 </template>
 
@@ -42,10 +167,13 @@ function injectPadding(e) {
   display: flex;
   flex-direction: column;
   align-items: center;
-  padding: 2rem;
   background: #f0f1f4;
 }
 
+.preview.landscape {
+  padding: 2rem;
+}
+
 .preview-header {
   display: flex;
   justify-content: space-between;
@@ -76,15 +204,14 @@ function injectPadding(e) {
 
 .preview-frame {
   width: 100%;
-  max-width: 900px;
   flex: 1;
   border: none;
   background: #fff;
-  box-shadow: 0 1px 8px rgba(0, 0, 0, 0.08);
 }
 
 .preview-frame.landscape {
   max-width: 1180px;
+  box-shadow: 0 1px 8px rgba(0, 0, 0, 0.08);
 }
 
 .empty-preview {
@@ -94,4 +221,209 @@ function injectPadding(e) {
   height: 100%;
   color: #5a6470;
 }
+
+.chat-fab {
+  position: fixed;
+  right: 1.5rem;
+  bottom: 1.5rem;
+  width: 52px;
+  height: 52px;
+  border: none;
+  border-radius: 50%;
+  background: #6366f1;
+  color: #fff;
+  font-size: 1.4rem;
+  cursor: pointer;
+  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.25);
+  z-index: 20;
+}
+
+.chat-fab:hover {
+  background: #4f46e5;
+}
+
+.chat-panel {
+  position: fixed;
+  right: 1.5rem;
+  bottom: 1.5rem;
+  width: 360px;
+  height: 500px;
+  max-height: calc(100vh - 3rem);
+  display: flex;
+  flex-direction: column;
+  background: #fff;
+  border: 1px solid #e2e5e9;
+  border-radius: 12px;
+  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.18);
+  z-index: 20;
+  overflow: hidden;
+}
+
+.chat-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 0.6rem 0.9rem;
+  background: #6366f1;
+  color: #fff;
+  font-weight: 600;
+  font-size: 0.9rem;
+}
+
+.chat-close {
+  border: none;
+  background: none;
+  color: #fff;
+  font-size: 1.4rem;
+  line-height: 1;
+  cursor: pointer;
+  padding: 0 4px;
+}
+
+.chat-messages {
+  flex: 1;
+  overflow-y: auto;
+  padding: 0.9rem;
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+}
+
+.chat-hint {
+  color: #9aa3af;
+  font-size: 0.82rem;
+  text-align: center;
+  margin-top: 1rem;
+}
+
+.chat-msg {
+  max-width: 85%;
+  padding: 7px 11px;
+  border-radius: 12px;
+  font-size: 0.85rem;
+  line-height: 1.4;
+  white-space: pre-wrap;
+  word-break: break-word;
+}
+
+.chat-msg.user {
+  align-self: flex-end;
+  background: #6366f1;
+  color: #fff;
+  border-bottom-right-radius: 3px;
+}
+
+.chat-msg.assistant {
+  align-self: flex-start;
+  background: #f1f3f7;
+  color: #1a1a1a;
+  border-bottom-left-radius: 3px;
+}
+
+.chat-typing {
+  color: #9aa3af;
+  font-style: italic;
+}
+
+.chat-msg.markdown :deep(p) {
+  margin: 0 0 0.5em;
+}
+
+.chat-msg.markdown :deep(p:last-child) {
+  margin-bottom: 0;
+}
+
+.chat-msg.markdown :deep(ul),
+.chat-msg.markdown :deep(ol) {
+  margin: 0.3em 0;
+  padding-left: 1.2em;
+}
+
+.chat-msg.markdown :deep(li) {
+  margin: 0.15em 0;
+}
+
+.chat-msg.markdown :deep(code) {
+  background: #e4e7ee;
+  padding: 1px 4px;
+  border-radius: 4px;
+  font-family: "SF Mono", Consolas, monospace;
+  font-size: 0.8em;
+}
+
+.chat-msg.markdown :deep(pre) {
+  background: #1e2330;
+  color: #e6e8ee;
+  padding: 8px 10px;
+  border-radius: 8px;
+  overflow-x: auto;
+  margin: 0.5em 0;
+}
+
+.chat-msg.markdown :deep(pre code) {
+  background: none;
+  padding: 0;
+  color: inherit;
+  font-size: 0.78em;
+}
+
+.chat-msg.markdown :deep(h1),
+.chat-msg.markdown :deep(h2),
+.chat-msg.markdown :deep(h3) {
+  font-size: 0.95em;
+  margin: 0.4em 0 0.2em;
+}
+
+.chat-msg.markdown :deep(a) {
+  color: #4f46e5;
+}
+
+.chat-msg.markdown :deep(table) {
+  border-collapse: collapse;
+  font-size: 0.95em;
+}
+
+.chat-msg.markdown :deep(th),
+.chat-msg.markdown :deep(td) {
+  border: 1px solid #d8dde3;
+  padding: 2px 6px;
+}
+
+.chat-input {
+  display: flex;
+  gap: 6px;
+  padding: 0.6rem;
+  border-top: 1px solid #e2e5e9;
+}
+
+.chat-input textarea {
+  flex: 1;
+  resize: none;
+  height: 38px;
+  padding: 8px 10px;
+  border: 1px solid #d8dde3;
+  border-radius: 8px;
+  font-size: 0.85rem;
+  font-family: inherit;
+  outline: none;
+}
+
+.chat-input textarea:focus {
+  border-color: #6366f1;
+}
+
+.chat-input button {
+  width: 38px;
+  border: none;
+  border-radius: 8px;
+  background: #6366f1;
+  color: #fff;
+  font-size: 1rem;
+  cursor: pointer;
+}
+
+.chat-input button:disabled {
+  opacity: 0.4;
+  cursor: not-allowed;
+}
 </style>