Express.js is a web framework for Node.js that simplifies building web servers and APIs. It provides tools for handling HTTP requests, defining routes, and sending responses. Its minimal design gives developers flexibility to organize applications according to their project’s needs.

Routing is a central feature of Express.js. Developers can define endpoints that respond to HTTP methods such as GET, POST, PATCH, and DELETE. These routes can handle tasks such as retrieving blog posts, creating user accounts, updating profiles, and deleting records.

Express.js uses middleware to process requests as they move through an application. Middleware functions can parse JSON data, check authentication, log requests, and handle errors. Developers can combine built-in middleware with custom functions and external packages to create organized request-processing flows.

Express.js can work with databases such as MongoDB and PostgreSQL through tools including Mongoose and Prisma. Combined with validation, authentication, and error handling, it provides a flexible foundation for backend development. It is useful for projects ranging from small REST APIs to the backend services supporting larger web applications.