Just as conventional institutions are organisationalstructures for coordinating the activities of multipleinteracting individuals, electronic institutions providea computational analogue for coordinating theactivities of multiple interacting software agents.In this paper, we argue that open multi-agent systemscan be effectively designed and implementedas electronic institutions, for which we provide acomprehensive computational model. More specifically,the paper provides an operational semanticsfor electronic institutions, specifying the essentialdata structures, the state representation and the keyoperations necessary to implement them.