React is a JavaScript library for building user interfaces, particularly single-page applications where UI updates are frequent. It allows developers to create reusable UI components that efficiently update in response to data changes, providing a declarative and efficient way to build interactive interfaces. Redux, on the other hand, is a state management library often used in conjunction with React. It helps manage the application state in a predictable manner by centralizing the state in a single store. Redux follows a unidirectional data flow, making it easier to track and manage changes in the application state, especially in complex applications with multiple components.