Protocols describe interactions among agents and thus underlie the engineering of multiagent systems. However, protocols are enacted by agents in physical systems. In particular, considerations of communication models and how distributed agents are able to make compatible choices would greatly affect whether a protocol may in fact be enacted successfully. The objective of this paper is to study the conceptual underpinnings of protocol enactment in multiagent systems. It seeks to characterize the operationalization of agents so as to determine whether and when agents may be interoperable.