Our application runs over 10,000 sustained transactions per second with a rich model. The key? Modeling state transitions explicitly. In today’s world many systems have non–functional requirements that prevent them from being single database centric. This presentation looks at how Domain Driven Design can fit into such environments including extremely large scale web sites, batch processing, and even using highly scalable backing stores such as CouchDb or HyperTable. Event streams, a different way of storing the current state of an object, open many doors in this session not only in how we scale and store our domain but also in how we rationalize about it.