Contrary to cognitive approaches of agency where a lot of effort is devoted to the formalization of agent concepts, little work has been done on the formalization of situated multi-agent systems (situated MASs). In this paper we present a generic model for situated MASs. This model formally describes an abstract architecture for situated MASs. In this architecture each agent is situated in its local context that it is able to perceive and in which it can act. Since intelligence in situated MASs results from the interactions of agents with the environment rather than from their individual capabilities, the model takes an action-centric approach. The model deals with (1) the actions of agents in the environment, (2) ongoing activities in the environment, such as moving objects, and (3) the interactions between agents and ongoing activities through the environment.