Event sourcing persists each entity as a sequence of state changing event. An entity’s current state is derived by replaying the events. Event sourcing is a great way to implement event-driven micro services. When one service updates an entity, the new events are consumed by other services, which then update their own state. In this talk we describe how to implement business logic using a domain model that is based on event sourcing. You will learn how to write functional, immutable domain models in Scala. We will compare and contrast a hybrid OO/FP design with a purely functional approach. You will learn how Domain Driven Design concepts such as bounded contexts and aggregates fit in with event-driven microservices.