It is observed that agent (or software agent) based systems largely imitate organizations of human actors. Thus, the nature of agent based systems can be better understood by first studying the ordinary human actors or organizations that own the agent based systems. In this chapter we first study agent systems and discuss characteristics of software agents, then we introduce a generic pattern of agents interaction derived from the communication patterns of human actors. Agent based systems are studied in the context of inter-organizational business process using diagrams and notations adapted by the authors. The methods and concepts used in this chapter are based on the Semiotics approach and the Language Action Perspective. For the illustration of our concept of agent based systems, we discuss a case study conducted based on a real life business.