Scala and its ecosystem of libraries have achieved a level of adoption that makes it increasingly challenging to make improvements. We can't just make changes to Scala and its popular libraries, because we need to think carefully about how to migrate existing user code. If the cost of migration becomes too great, users may chose to delay upgrading, or opt not upgrade at all. In this talk, Bill Venners will explain how we can balance the value of making improvements to the Scala language and libraries with that of maintaining stability and compatibility. He will make the case that it is possible and desirable to make improvements despite having users, and show how accomplish it.S