Boundary Objects (BOs) and Coordination Mechanisms (CMs) are terms with a long history in CSCW. They have both been used widely since their initial definition. We find the concepts used in the same settings to describe some form of collaboration among different peoples or group of people. Sometimes it seems that the choice of concepts has not been thought through. Thus, in this paper, we give a detailed description of both concepts, and then we discuss them side by side by highlighting six issues that researchers should take in consideration before defining an object as a coordination mechanism or a boundary object.