This document introduces Node.js and its suitability for building web applications. Node.js uses an asynchronous and non-blocking I/O model that makes it performant for building real-time and I/O intensive apps. It has a large library ecosystem and frameworks like Express make app development fast. Node.js uses a single thread with background worker threads for non-blocking I/O. Popular modules discussed include Connect for modular web apps and Passport.js for authentication.