Redux.js is a JavaScript library for managing application state in a predictable way. It stores shared data in a central store, allowing different parts of an application to access consistent information. This is useful for features such as shopping carts, user preferences, and workflows involving multiple screens.

Redux follows a structured process for updating state. An action describes what happened, and a reducer determines how the state should change. Components dispatch actions and subscribe to relevant data from the store, helping keep state changes organized and easier to trace.

Redux Toolkit simplifies writing Redux logic. It provides utilities for configuring a store, creating slices, and handling updates with less repetitive code. Its integration with Immer allows developers to write updates using mutation-like syntax while producing immutable state changes.

Redux can work with different interface libraries, and React applications commonly connect to it through React Redux. However, not every piece of data needs to be stored globally. Keeping simple interface state within components and using Redux for shared application state can make a project easier to understand and maintain.