Following our own experience developing a concurrent object-oriented language as well of that of other researchers, we have identified several key problems in the design of a concurrency model compatible with the mechanisms of object-oriented programming. We propose an approach to language design in which an executable notation describing the behaviour of communicating agents is extended by syntactic patterns that encapsulate language constructs. We indicate how various language models can be accommodated, and how mechanisms such as inheritance can be modeled. Finally, we introduce a new notion of types that characterizes concurrent objects in terms of their externally visible behaviour.