React is an open-source JavaScript library developed by Facebook for building user interfaces, particularly for single-page applications. It allows developers to create reusable UI components, making the development process more efficient and organized. Since its release in 2013, React has become one of the most popular libraries for front-end development.

React promotes a component-based architecture, where the UI is divided into independent, reusable pieces called components. This modular approach makes it easier to manage and maintain code, as each component can be developed and tested in isolation.

React uses a Virtual DOM to optimize rendering performance. Instead of directly manipulating the browser's DOM, React creates a lightweight copy of the DOM in memory. When changes occur, React updates the Virtual DOM first, calculates the differences, and then efficiently updates the actual DOM, resulting in faster performance.

React allows developers to describe what the UI should look like for a given state, rather than how to achieve that state. This declarative approach makes the code more predictable and easier to debug.

In React, data flows in one direction, from parent components to child components. This unidirectional data flow simplifies the data management process and makes it easier to understand how data changes affect the UI.

React has a vast ecosystem of libraries and tools that enhance its functionality. Popular libraries like React Router for routing and Redux for state management complement React, allowing developers to build complex applications with ease.