Reselect is a powerful library for creating memoized, composable selectors in React and Redux applications. It's an invaluable tool for any developer who wants to optimize the performance of their React or Redux application. With Reselect, you can create composable selectors that are both efficient and easy to maintain. It allows you to keep your application's data organized and up to date by returning the same result for the same input, and provides a flexible API for creating complex selectors. Reselect is an essential library for any developer looking to get the most out of React or Redux.