Frontend libraries are collections of pre-written code that help developers build user interfaces for websites and applications. They provide reusable components and functions, making it easier to create interactive and visually appealing designs without starting from scratch. Popular frontend libraries include React, Vue.js, and jQuery. These libraries streamline the development process by offering tools for managing state, handling events, and manipulating the Document Object Model (DOM). By using frontend libraries, developers can save time, improve code quality, and enhance the overall user experience of their projects.