Conformity by an agent to a convention to which the agent is a party is rational only if the agent prefers to conform given the other parties conform and believes the others will conform. But this justification is inadequate; what, for example, is the justification for this belief? The required rational justification requires recourse to (a) preferences for general conformity (as opposed to merely conditional preferences for one's own conformity) and (b) procedures. An agent adopts a procedure when he chooses to perform a whole set of future actions, as opposed to a single action.