Concurrent object languages are in many respects the ancestors of agent languages. The notion of a self-contained concurrently executing object, with some internal state that is not directly accessible to the outside world, responding to messages from other such objects, is very close to the concept of an agent as we have defined it. The earliest concurrent object framework was Hewitt's Actor model [Agha, 1986][Hewitt, 1977]; another well-known example is the ABCL system [Yonezawa, 1990]. For a discussion on the relationship between agents and concurrent object programming, see [Gasser and Briot, 1992].