diff --git a/src/cli.ts b/src/cli.ts
index 9fb592e..0382229 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -222,7 +222,7 @@ export function helpPage() {
 	const options = optionsOrder.map((key) => CLI_OPTIONS[key]);
 
 	const section = (heading: string = '', lines: string[] = []) => {
-		const result = [];
+		const result: string[] = [];
 		if (heading.length) result.push(indent + color.style(heading, 'bold'));
 		if (lines.length) result.push(lines.map((l) => indent.repeat(2) + l).join('\n'));
 		return result.join('\n\n');
diff --git a/src/handler.ts b/src/handler.ts
index 5942c37..2176bf1 100644
--- a/src/handler.ts
+++ b/src/handler.ts
@@ -175,6 +175,7 @@ export class RequestHandler {
 		const body = dirListPage({
 			root: this.#options.root,
 			ext: this.#options.ext,
+			urlMount: urlMountPath(this.#req),
 			urlPath: this.urlPath ?? '',
 			filePath,
 			items,
@@ -393,3 +394,18 @@ function parseHeaderNames(input: string = ''): string[] {
 		.map((h) => h.trim())
 		.filter(isHeader);
 }
+
+export function urlMountPath({
+	baseUrl,
+	originalUrl,
+	url,
+}: Pick<Request, 'baseUrl' | 'originalUrl' | 'url'>): string | undefined {
+	const trim = (p = '') => (p.length > 1 ? trimSlash(p, { end: true }) : p);
+	if (typeof baseUrl === 'string') {
+		return trim(baseUrl);
+	} else if (typeof url === 'string' && typeof originalUrl === 'string') {
+		if (url === '' || url === '/') return trim(originalUrl);
+		const lastIndex = originalUrl.lastIndexOf(url);
+		if (lastIndex > 0) return trim(originalUrl.slice(0, lastIndex));
+	}
+}
diff --git a/src/index.ts b/src/index.ts
index e69de29..a6fb620 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -0,0 +1,39 @@
+import { RequestHandler } from './handler.ts';
+import { serverOptions } from './options.ts';
+import { FileResolver } from './resolver.ts';
+import type { Request, Response, ServerOptions } from './types.d.ts';
+import { errorList } from './utils.ts';
+
+export function middleware(options: Partial<ServerOptions>) {
+	if (!options || typeof options !== 'object') {
+		options = {};
+	}
+
+	const onError = errorList();
+	const fullOptions = serverOptions(
+		{ root: typeof options.root === 'string' ? options.root : '', ...options },
+		onError,
+	);
+	if (onError.list.length) {
+		throw new OptionsError(onError.list);
+	}
+
+	const resolver = new FileResolver(fullOptions);
+
+	return async function servitsyHandler(req: Request, res: Response, next: (value: any) => void) {
+		const handler = new RequestHandler({ req, res, resolver, options: fullOptions });
+		await handler.process();
+		if (res.statusCode !== 200 && !res.headersSent && typeof next === 'function') {
+			next(handler.data());
+		}
+	};
+}
+
+class OptionsError extends Error {
+	list: string[];
+	constructor(list: string[]) {
+		const message = 'Invalid option(s):\n' + list.map((msg) => `    ${msg}`).join('\n');
+		super(message);
+		this.list = [...list];
+	}
+}
diff --git a/src/pages.ts b/src/pages.ts
index ab9c48f..7d7965a 100644
--- a/src/pages.ts
+++ b/src/pages.ts
@@ -57,17 +57,26 @@ export function errorPage(data: { status: number; url: string; urlPath: string |
 
 export function dirListPage(data: {
 	root: string;
+	urlMount?: string;
 	urlPath: string;
 	filePath: string;
 	items: FSLocation[];
 	ext: string[];
 }) {
-	const { root, urlPath, filePath, items, ext } = data;
+	const { root, urlMount, urlPath, filePath, items, ext } = data;
+
 	const rootName = basename(root);
-	const trimmedUrl = trimSlash(urlPath);
+	const trimmedUrl = [urlMount, urlPath]
+		.map((s) => s && trimSlash(s))
+		.filter(Boolean)
+		.join('/');
 	const baseUrl = trimmedUrl ? `/${trimmedUrl}/` : '/';
 
-	const displayPath = decodeURIPathSegments(trimmedUrl ? `${rootName}/${trimmedUrl}` : rootName);
+	let displayPath = decodeURIPathSegments(trimmedUrl ? `${rootName}/${trimmedUrl}` : rootName);
+	if (urlMount && urlMount.length > 1) {
+		displayPath = decodeURIPathSegments(trimmedUrl);
+	}
+
 	const parentPath = dirname(filePath);
 	const showParent = trimmedUrl !== '';
 
diff --git a/src/types.d.ts b/src/types.d.ts
index 708d50f..e10fae3 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -1,5 +1,11 @@
-export type Request = import('node:http').IncomingMessage & { originalUrl?: string };
-export type Response = import('node:http').ServerResponse<Request>;
+import type { IncomingMessage, ServerResponse } from 'node:http';
+
+export type Request = IncomingMessage & {
+	baseUrl?: string;
+	originalUrl?: string;
+};
+
+export type Response = ServerResponse<Request>;
 
 export type FSKind = 'dir' | 'file' | 'link' | null;
 
diff --git a/test/handler.test.ts b/test/handler.test.ts
index 7a08920..df46ef8 100644
--- a/test/handler.test.ts
+++ b/test/handler.test.ts
@@ -2,7 +2,13 @@ import { IncomingMessage, ServerResponse } from 'node:http';
 import { Duplex } from 'node:stream';
 import { afterAll, expect, suite, test } from 'vitest';
 
-import { extractUrlPath, fileHeaders, isValidUrlPath, RequestHandler } from '../src/handler.ts';
+import {
+	extractUrlPath,
+	fileHeaders,
+	isValidUrlPath,
+	RequestHandler,
+	urlMountPath,
+} from '../src/handler.ts';
 import { FileResolver } from '../src/resolver.ts';
 import type { HttpHeaderRule, ServerOptions } from '../src/types.d.ts';
 import { fsFixture, getBlankOptions, getDefaultOptions, platformSlash } from './shared.ts';
@@ -418,3 +424,21 @@ suite('RequestHandler', async () => {
 		});
 	});
 });
+
+suite('urlMountPath', () => {
+	test('is undefined when baseUrl and originalUrl are undefined', () => {
+		expect(urlMountPath({})).toBe(undefined);
+		expect(urlMountPath({ url: '/hello/world' })).toBe(undefined);
+	});
+
+	test('returns the baseUrl when present (express 4+)', () => {
+		expect(urlMountPath({ baseUrl: '/' })).toBe('/');
+		expect(urlMountPath({ baseUrl: '/hello' })).toBe('/hello');
+		expect(urlMountPath({ baseUrl: '/hello/' })).toBe('/hello');
+	});
+
+	test('infers the baseUrl from url and originalUrl (express 3)', () => {
+		expect(urlMountPath({ originalUrl: '/', url: '/' })).toBe('/');
+		expect(urlMountPath({ originalUrl: '/static/index.html', url: '/index.html' })).toBe('/static');
+	});
+});