Is economics of conventions an instrumental approach of individual rationality ? Economics of conventions proposes a particularly stimulating research project which puts the stress on the analysis of the rules' and conventions' roles in the economic coordination. To be coherent, this project requires to be based on a theory of the emergence and dynamics of conventions. However, as a feedback effect, this theory raises questions about the hypothesis of rationality that should to be attributed to actors. The hypothesis of limited rationality at the basis of economics of conventions, is ambiguous. It especially covers highly diverging hypotheses concerning the exclusively or non exclusively instrumental characteristic of individual rationalit...