Agentis is a framework for building interactive multiagent applications which is based upon a model of agent interaction whose key elements are services and tasks. Central to the operation of the system is the set of protocols that permit reliable, concurrent request and provision of services and tasks from and to agents, using an underlying asynchronous point-to-point messaging infrastructure. In this paper we focus on this aspect of the Agentis system and provide a detailed description of these protocols, together witha formalspecificationin Z. The specificationcan be seen as part of a more complete formal specification of the entire system, which provides an integratedandcoherent way of describing the system at different levels. In so specifying the Agentis protocols, however, we also provide some general guidelines which may be appliedto the specification of other protocols for agent interaction.