Parties neither cease to exist nor cease to compete for office when the general election is over. Instead, a new round of competition begins, with legislators as voters and party leaders as candidates. The offices at stake are what we call “mega-seats.” We consider the selection of three different types of mega-seats—cabinet portfolios, seats on directing boards, and permanent committee chairs—in 57 democratic assemblies. If winning parties select the rules by which mega-seats are chosen and those rules affect which parties can attain mega-seats (one important payoff of “winning”), then parties and rules should coevolve in the long run. We find two main patterns relating to legislative party systems and a country's length of experience with democratic governance.