JavaScript libraries are collections of pre-written JavaScript code that help developers create interactive web applications more efficiently. They provide reusable functions and components, allowing developers to focus on building features rather than writing code from scratch. Popular libraries like jQuery and React simplify tasks such as DOM manipulation and state management. These libraries enhance the functionality of websites and applications, making them more dynamic and user-friendly. By leveraging these tools, developers can improve their productivity and maintainability of their code. As the web continues to evolve, JavaScript libraries remain essential for modern web development.