Collective decision making frequently involves voting, but voting rules are not always the same. Sometimes a consen­sus is required, sometimes a simple majority is enough and sometimes a qualified majority is required. In the sphere of economics as well – in markets and in companies – many different rules are at work. In some markets sellers set prices unilaterally, some markets are governed by auctions and in yet other markets prices are determined through bargaining. The mechanism design theory helps us understand which rules of play yield the best results in both the political and economic sphere.