In this article the foundations for software agents and agent systems will be laid from the point of view of Engineering Sciences by applying the basics of software architecture. For architecture modeling an object-oriented approach will be used. The components of an agent system will be mapped on to object-oriented model types. With the help of objectoriented methods special model types for interactions and adaptivity serving re-use will be derived. The sound theoretical considerations about software agents and agent systems and their object-oriented modeling and specification support and extend the functions described in the standardizations.