This paper deals with coordination in the context of loose Inter-Organizational Workflow (IOW). The aim of IOW is to support the cooperation between business processes running in different organizations. Loose IOW refers to occasional cooperation between organizations, free of structural constraints, where the organizations involved and their number are not predefined. This paper shows that the agent technology is appropriate to coordinate business processes in the context of loose IOW. More precisely, this paper proposes an agent-oriented architecture, compliant with the Workflow Management Coalition reference architecture, which represents business processes as agents and uses mediators to coordinate them. This paper also defines an agent-oriented organizational model that describes the business processes coordination according to the Agent-Group-Role meta model.