Political scientists have long classified systems of government as parliamentary or presidential, two-party or multiparty, and so on. But such distinctions often fail to provide useful insights. For example, how are we to compare the United States, a presidential bicameral regime with two weak parties, to Denmark, a parliamentary unicameral regime with many strong parties? Veto Players advances an important, new understanding of how governments are structured. The real distinctions between political systems, contends George Tsebelis, are to be found in the extent to which they...