Express.js is a minimal and flexible web application framework for Node.js. It provides a robust set of features for building web and mobile applications, allowing developers to create APIs and manage server-side logic efficiently. With its simple syntax and middleware support, Express.js streamlines the process of handling requests and responses. One of the key benefits of using Express.js is its ability to integrate with various databases and third-party services. This makes it a popular choice for developers looking to build scalable and maintainable applications. Its active community and extensive documentation further enhance its usability and support.