Back-end developers are responsible for building and maintaining the server-side of web applications. They work with databases, server logic, and application programming interfaces (APIs) to ensure that everything functions smoothly behind the scenes. Their primary goal is to create a seamless experience for users by managing data and ensuring that the front-end can communicate effectively with the back-end. These developers typically use programming languages such as Python, Java, or Ruby to write code. They also work with frameworks like Node.js or Django to streamline development. By focusing on the back-end, they enable front-end developers to create visually appealing and interactive user interfaces.