Interfaces in C# help us create loosely coupled code that is easier to maintain, update, and test. But do you really know C# interfaces? Interfaces have changed over the years, and many the changes were not well publicized -- including default implementation, member access modifiers, and static members. The Microsoft documentation is correct, but many other C# resources have outdated information. So let's look at these features and see where they are useful and where they should be avoided. With some practical tips, "gotchas", and plenty of examples, we'll see how to use these features effectively (and safely) in our code.