Research in political behavior has increasingly turned to the cognitions underlying attitudes. The simplest of these cognitions are political facts - the bits of information about politics that citizens hold. While other key concepts in political science - partisanship, trust, tolerance - have widely used (if still controversial) measures that facilitate comparisons across time and among studies, the discipline has no generally accepted measure of the public's level of political information. This paper describes the development and testing of survey-based measures of political knowledge, with special attention to the existing items on the National Election Study surveys. In so doing, it illustrates the use of a variety of techniques for item analysis and scale construction. We also present a recommended five-item knowledge index.