Top-Down Testing is a software testing approach that starts with testing the higher-level components of a system before moving down to the lower-level components. In this method, the main functionality is tested first, allowing testers to identify issues in the overall system architecture and design. This approach often uses stubs to simulate lower-level modules that have not yet been developed. By focusing on the top layers, Top-Down Testing helps ensure that the core features work as intended before delving into the details. This can lead to early detection of integration issues and improve the efficiency of the testing process, as problems can be addressed before they propagate to lower levels.