Redux is a state management library commonly used with React. It provides a predictable state container for JavaScript applications, making it easier to manage the state of an application and keep it in sync with the user interface. With Redux, the application's state is stored in a single JavaScript object called the 'store'. The store holds the state of the entire application and allows components to access and update the state in a predictable manner. Actions are dispatched to the store to trigger updates to the state, and reducers specify how the state should be updated based on these actions. Redux uses a unidirectional data flow, which means that data flows in a single direction within the application. This makes it easier to understand how the state changes over time and helps prevent common issues like race conditions and inconsistent state. By using Redux, developers can write more predictable and maintainable code, as the state management logic is separate from the UI components. It also enables features like time travel debugging, where developers can replay past actions and see how the state of the application evolves.