TDD involves intentionally writing a failing test, writing the minimum amount of application code that allows the test to pass, and running the test again to ensure it passes. BDD uses the same principles as TDD but applies them on a larger scale by asking what the purpose of a feature or application is, writing acceptance criteria, and then writing the code to ensure that the application fulfills those criteria. This approach prioritizes cross-team communication, making it well-suited for applications requiring a bigger picture perspective. In contrast, TDD is often led by a sole developer and requires more technical knowledge, making it better suited for smaller units of code where testing can be more manageable. The choice between TDD and BDD depends on the project's scope, team size, and communication needs.