diff --git a/Dockerfile b/Dockerfile
index 32e92bf..29dea3c 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,6 +6,10 @@ RUN npm ci --omit=dev && mkdir /app/screenshot-cache && chown node:node /app/scr
 COPY server.mjs ./server.mjs
 COPY screenshot-cache.mjs ./screenshot-cache.mjs
 COPY public ./public
+RUN mkdir -p public/vendor/prism \
+    && cp node_modules/prismjs/components/prism-core.min.js public/vendor/prism/ \
+    && cp node_modules/prismjs/components/prism-asm6502.min.js public/vendor/prism/ \
+    && cp node_modules/prismjs/LICENSE public/vendor/prism/LICENSE
 COPY . /programs
 
 ENV PORT=8080
diff --git a/package-lock.json b/package-lock.json
index d1421b3..10660ae 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -6,6 +6,7 @@
     "": {
       "name": "c64-program-collection",
       "dependencies": {
+        "prismjs": "1.30.0",
         "sharp": "0.35.5"
       }
     },
@@ -528,6 +529,15 @@
         "node": ">=8"
       }
     },
+    "node_modules/prismjs": {
+      "version": "1.30.0",
+      "resolved": "https://registry.npmjs.org/prismjs/-/prismjs-1.30.0.tgz",
+      "integrity": "sha512-DEvV2ZF2r2/63V+tK8hQvrR2ZGn10srHbXviTlcv7Kpzw8jWiNTqbVgjO3IY8RxrrOUF8VPMQQFysYYYv0YZxw==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=6"
+      }
+    },
     "node_modules/semver": {
       "version": "7.8.5",
       "resolved": "https://registry.npmjs.org/semver/-/semver-7.8.5.tgz",
diff --git a/package.json b/package.json
index 5c00031..c56c2d5 100644
--- a/package.json
+++ b/package.json
@@ -2,5 +2,5 @@
   "name": "c64-program-collection",
   "private": true,
   "type": "module",
-  "dependencies": { "sharp": "0.35.5" }
+  "dependencies": { "sharp": "0.35.5", "prismjs": "1.30.0" }
 }
diff --git a/public/app.js b/public/app.js
index af0eab6..a19e7dc 100644
--- a/public/app.js
+++ b/public/app.js
@@ -207,7 +207,7 @@ async function showSource(program) {
   try {
     const response = await fetch(`/api/source?path=${encodeURIComponent(program.path)}`, { cache: 'no-store' });
     if (!response.ok) throw new Error('The program source could not be loaded.');
-    sourceCode.querySelector('code').textContent = await response.text();
+    highlightSource(sourceCode.querySelector('code'), program, await response.text());
     sourceStatus.hidden = true;
     sourceCode.hidden = false;
   } catch (error) {
@@ -273,7 +273,7 @@ async function loadInlineSource(program) {
   try {
     const response = await fetch(`/api/source?path=${encodeURIComponent(program.path)}`, { cache: 'no-store' });
     if (!response.ok) throw new Error('The program source could not be loaded.');
-    listing.querySelector('code').textContent = await response.text();
+    highlightSource(listing.querySelector('code'), program, await response.text());
     message.hidden = true;
     listing.hidden = false;
   } catch (error) {
diff --git a/public/index.html b/public/index.html
index edf8098..b97c23a 100644
--- a/public/index.html
+++ b/public/index.html
@@ -90,6 +90,9 @@
     <p id="source-status" class="status">Loading source…</p>
     <pre id="source-code" hidden><code></code></pre>
   </dialog>
+  <script src="/vendor/prism/prism-core.min.js" data-manual></script>
+  <script src="/vendor/prism/prism-asm6502.min.js"></script>
+  <script src="/source-highlighting.js"></script>
   <script src="/app.js"></script>
 </body>
 </html>
diff --git a/public/source-highlighting.js b/public/source-highlighting.js
new file mode 100644
index 0000000..48599ea
--- /dev/null
+++ b/public/source-highlighting.js
@@ -0,0 +1,28 @@
+/* Prism grammars tailored to the sources in this collection. */
+if (window.Prism) {
+  Prism.languages['c64-basic'] = {
+    'string': { pattern: /"[^"\r\n]*(?:"|(?=\r?$))/m, greedy: true },
+    'comment': { pattern: /\bREM[^\r\n]*/i, greedy: true },
+    'line-number': { pattern: /^\d+/m, alias: 'number' },
+    'keyword': /\b(?:CLOSE|CLR|CMD|CONT|DATA|DEF|DIM|END|FN|FOR|GET|GOSUB|GOTO|IF|INPUT|LET|LIST|LOAD|NEW|NEXT|ON|OPEN|POKE|PRINT|READ|RESTORE|RETURN|RUN|SAVE|STEP|STOP|SYS|THEN|TO|VERIFY|WAIT)\b/i,
+    'function': /\b(?:ABS|ASC|ATN|CHR\$|COS|EXP|FRE|INT|LEFT\$|LEN|LOG|MID\$|PEEK|POS|RIGHT\$|RND|SGN|SIN|SPC|SQR|STR\$|TAB|TAN|USR|VAL)(?=\s*\()/i,
+    'number': /(?:\b\d+(?:\.\d*)?|\B\.\d+)(?:E[+-]?\d+)?/i,
+    'operator': /[+\-*/^=<>]|\b(?:AND|NOT|OR)\b/i,
+    'punctuation': /[,;:()]/
+  };
+  Prism.languages['acme-6502'] = Prism.languages.extend('asm6502', {
+    'directive': { pattern: /!\w+\b|\.\w+(?=\s)/, alias: 'property' },
+    'operator': /[+\-*/=<>#&|^~]/
+  });
+  Prism.languages.insertBefore('acme-6502', 'op-code', {
+    'label': { pattern: /^\s*[a-z_]\w*(?=:)/im, alias: 'function' }
+  });
+}
+
+function highlightSource(element, program, source) {
+  const language = program.language === 'machine-code' ? 'acme-6502' : 'c64-basic';
+  element.className = `language-${language}`;
+  // Assign text before highlighting, so source cannot inject HTML.
+  element.textContent = source;
+  if (window.Prism) Prism.highlightElement(element);
+}
diff --git a/public/styles.css b/public/styles.css
index c2e79c9..9276ce2 100644
--- a/public/styles.css
+++ b/public/styles.css
@@ -85,6 +85,15 @@ button:disabled { opacity: .5; cursor: wait; }
 .instructions-panel h2, .program-source-panel h2 { margin: 0 0 .85rem; font-size: 1rem; letter-spacing: .08em; text-transform: uppercase; }
 .program-source-panel pre { max-height: 600px; margin: 0; padding: 1rem; overflow: auto; border-radius: 6px; background: #0d0928; color: #d8d3f4; font: .85rem/1.55 ui-monospace, SFMono-Regular, Consolas, monospace; white-space: pre; tab-size: 4; }
 .program-source-panel pre:focus-visible { outline: 2px solid var(--c64-light-blue); outline-offset: 2px; }
+.program-source-panel code, .source-modal code { font: inherit; }
+.token.comment { color: #aaa5b8; font-style: italic; }
+.token.keyword { color: #c6b4ff; }
+.token.string { color: #a6e3ad; }
+.token.number { color: #f9c88b; }
+.token.function { color: #8bd5ef; }
+.token.property { color: #f5bde6; }
+.token.variable { color: #eed49f; }
+.token.operator, .token.punctuation { color: #cad3f5; }
 .control-list { display: grid; gap: .7rem; }
 .control-row { display: grid; grid-template-columns: minmax(150px, auto) 1fr; gap: 1rem; align-items: center; color: #d2cef0; }
 .key-group { display: flex; flex-wrap: wrap; gap: .35rem; }