Communication protocols are widely recognized as essential to an efficient coordination among agents. Accordingly, this paper proposes to consider protocols as first-class entities, so that an agent that wants to initiate a conversation creates an instance of the appropriate protocol, called a Moderator, in charge of managing this conversation. Then, agents intending to take part in the Conversation send their communication actions to the Moderator, which guarantees the respect of the protocol's rules. Cooperative Objects, a High-Level Petri Net language, may be used to specify, validate and implement Moderators. From a Software Engineering point of view, the resulting MAS architecture features many advantages.