We made some nice progress in this chapter on such a complex topic as concurrency. You learned about actors, what problems they solve, and how to create and use them. You also learned about how a pool of threads works with actors, how to communicate between actors, and most important, how isolated mutability comes to the rescue. We also applied these concepts to implement a practical example that showed substantial speed improvement with only a small amount of code. In the next part, we’ll look at applying various concepts of Scala we’ve explored throughout this book.