Testing Library is a popular JavaScript library designed to help developers test user interfaces in a way that resembles how users interact with applications. It encourages writing tests that focus on the behavior of the application rather than the implementation details, making tests more reliable and easier to maintain. The library provides a set of utilities for querying and interacting with DOM elements, allowing developers to simulate user actions like clicking buttons or filling out forms. By promoting best practices in testing, Testing Library helps ensure that applications are user-friendly and function as intended across different scenarios.