Hybrid is an object-oriented programming language in which objects are the active entities. Active objects in Hybrid are both concurrent and persistent, thus unifying the notion of an "object" with that of processes and files. Hybrid introduces the concept of an activity as a means for controlling the interactions between active objects. The language provides constructs that allow one to restrict or relax this control in a fairly simple way. In particular, mechanisms for delaying and "delegating" activities are provided. Furthermore, Hybrid is designed so as to provide powerful constructs for reusing code in a way that is consistent with strong-typing.