You want code that is easy to maintain, extend, and test. C# interfaces are here to help. In this session, you will learn we to use interfaces effectively in your code, starting at the beginning ("What are interfaces?") and then exploring why and when to use them. Along the way you'll learn how to use existing interfaces, implement your own interfaces, and also use interfaces for unit testing and dependency injection. The result is code that is easier to maintain, extend, and test.