The paper introduces the Multilayered Multi--Agent Situated System (MMASS). The MMASS allows tha description of situated agents that is, agents sensitive to the spatial relationships that determine constraints and abilities for actions as well as privileged cooperation relationships. The main feature of the MMASS model is to give an explicit definition of the spatial structure of the environment in which the system of situated agents acts and interacts. Agent environment, possibly multilayered, can reproduce a physical space. It is nevertheless possible to define a `virtual space' that agents can roam and where they interact. Interactions take place when two or more agents are brought into dynamic spatial relationship through a set of reciprocal actions, and have an influence on the future behavior of the agents. There are several application domains that require the representation of the space in order to take advantage in the multi--agent approach. Typical examples of these domains are the Multi--Agent Based Simulation (MABS) and the Computer Supported Cooperative Work (CSCW). Two specific problems of these domains will be used in the paper to illustrate the MMASS model.