A club’s majority rule defines the number of members that must approve a policy proposed to replace the status quo. Since the majority rule thus dictates the extent to which winners must compensate losers, it also determines the incentives to invest in order to become a winner of anticipated projects. If the required majority is large, members invest too little because of a holdup problem; if it is small, members invest too much in order to become a member of the majority coalition. To balance these opposing forces, the majority rule should increase in the project’s value and the club’s enforcement capacity but decrease in the heterogeneity in preferences. Externalities can be internalized by adjusting the rule. With heterogeneity in size or initial conditions, votes should be appropriately weighted or double majorities required.