We now discuss the actor model of concurrent computing. The actor model is used extensively in many real-world applications such as Facebook or X (Twitter), but it is not widely used in scientific computing. We start this chapter by providing the motivation for the use of the actor model in scientific computing. Then we introduce the basic concepts surrounding the actor model with examples using the C++ Actor Framework (CAF). We build upon the basics to demonstrate how the actor model is fault-tolerant and introduce how it can be leveraged in distributed systems. Finally, we finish this chapter by exposing some of the “hidden details” and other advanced features common within actor model implementations that are taken care of automatically.