It is well recognized that Agent Communication Languages (ACL’s) are a critical element of Multi-Agent Systems and a key to their successful application in commerce and industry. The field of protocol engineering, which addresses the problems of specifying and verifying machine communication languages and testing implementations, has developed powerful theoretical and automated techniques for doing this, and more importantly, a mature understanding of the requirements that communication language and protocol specifications should meet. Unfortunately, those developing and promulgating ACL’s appear not to have taken advantage of this body of knowledge. An examination of the current ACL specifications being developed by the Foundation for Intelligent Physical Agents (FIPA) reveals a confusing amalgam of different formal and informal specification techniques whose net result is ambiguous, inconsistent and certainly under-specified. Allowances must be made, as these are draft specifications, but rather than providing a verified foundation for reliable communication between heterogeneous agents, they seem likely to lead to a host of unreliable and incompatible implementations, or to be ignored in favour of more pragmatic and robust approaches. In this paper, we propose a set of requirements against which an ACL specification can be judged, briefly explore some of the shortcomings of the FIPA ACL and their origins, and contrast it with a small ACL which was designed with reliability and ease of verification as prime objectives.