diff --git a/.changeset/lovely-lemons-fold.md b/.changeset/lovely-lemons-fold.md
new file mode 100644
index 0000000..8547398
--- /dev/null
+++ b/.changeset/lovely-lemons-fold.md
@@ -0,0 +1,5 @@
+---
+"ember-showdown-shikiji": minor
+---
+
+feat: add theme and language config options
diff --git a/README.md b/README.md
index b749ce8..b719d7f 100644
--- a/README.md
+++ b/README.md
@@ -58,6 +58,25 @@ module.exports = function () {
 };
 ```
 
+### Configuration
+
+In `config/environment.js` you can configure the following options:
+
+```js
+module.exports = function (environment) {
+  const ENV = {
+    // Other options ...
+    'ember-showdown-shikiji': {
+      theme: 'github-dark', // The theme to use for highlighting
+      languages: ['javascript', 'handlebars'], // The languages to highlight
+    },
+  };
+  return ENV;
+};
+```
+
+By default the theme used is `dark-plus` and all languages are loaded.
+
 ## Contributing
 
 See the [Contributing](CONTRIBUTING.md) guide for details.
diff --git a/ember-showdown-shikiji/src/initializers/showdown-shikiji.ts b/ember-showdown-shikiji/src/initializers/showdown-shikiji.ts
index a33d8b3..3ba19d8 100644
--- a/ember-showdown-shikiji/src/initializers/showdown-shikiji.ts
+++ b/ember-showdown-shikiji/src/initializers/showdown-shikiji.ts
@@ -10,10 +10,10 @@ import { glimmerHandlebarsGrammar } from '../glimmer-handlebars-grammar.ts';
 const CODE_BLOCK_REGEX =
   /(?:^|\n)(?: {0,3})(```+|~~~+)(?: *)([^\n`~]*)\n([\s\S]*?)\n(?: {0,3})\1/g;
 
-async function initializeShikiji() {
+async function initializeShikiji(theme: string, languages: string[]) {
   const highlighter = await getHighlighter({
-    themes: ['dark-plus'],
-    langs: [glimmerHandlebarsGrammar, ...Object.keys(bundledLanguages)],
+    themes: [theme],
+    langs: [glimmerHandlebarsGrammar, ...languages],
   });
 
   return highlighter;
@@ -86,7 +86,7 @@ function transformCodeBlock(
   codeblock = codeblock.replace(/\n+$/g, ''); // trim trailing whitespace
 
   const { language, attributes } = extractCodeBlockHeader(languageBlock);
-  const shikijiLanguage = Object.keys(bundledLanguages).includes(language)
+  const shikijiLanguage = highlighter.getLoadedLanguages().includes(language)
     ? language
     : 'text';
 
@@ -97,7 +97,7 @@ function transformCodeBlock(
 
   codeblock = highlighter.codeToHtml(codeblock, {
     lang: shikijiLanguage,
-    theme: 'dark-plus',
+    theme: highlighter.getLoadedThemes()[0]!,
     transformers: [transformerNotationDiff()],
   });
   codeblock = codeblock.replace(
@@ -132,7 +132,13 @@ function transformCodeBlock(
 
 export async function initialize(application: Application) {
   application.deferReadiness();
-  const highlighter = await initializeShikiji();
+
+  const config = application.resolveRegistration('config:environment') as {
+    'ember-showdown-shikiji'?: { theme?: string; languages?: string[] };
+  };
+  const { theme = 'dark-plus', languages = Object.keys(bundledLanguages) } =
+    config['ember-showdown-shikiji'] ?? {};
+  const highlighter = await initializeShikiji(theme, languages);
 
   showdown.subParser('githubCodeBlocks', function (text, options, globals) {
     // Early exit if option is not enabled