C++ libraries are collections of pre-written code that developers can use to perform common tasks without having to write everything from scratch. These libraries provide functions, classes, and templates that simplify programming in C++. Examples include the Standard Template Library (STL), which offers data structures and algorithms, and Boost, which provides additional functionality for various programming needs. Using C++ libraries can significantly speed up the development process and improve code quality. They allow programmers to leverage existing solutions, ensuring that their applications are built on tested and optimized code. This practice enhances productivity and encourages code reuse across different projects.