B. Chaib-draa Dept. Informatique, Fac. Sciences Universite Laval, Ste-Foy, Canada, G1K 7P4 ABSTRACT This paper proposes to see agent communication language (ACL) as a joint activity and not as the sum of the speaker's and hearer's (speech) acts. In this paper, a conversation in the context of ACL is viewed as a {\em joint activity} which can be realized as sequences of smaller actions, many of which are themselves joint actions. Social agents which participate to this joint activity have to coordinate their joint actions. In each joint act, the participants face a coordination problem: which actions are expected? The answer to this question proposed here, is based on complex notions as collective intention, joint plan, joint commitments and the notion of common ground.