While government turnover is often thought of as an adverse source of instability, it may also be viewed as a favourable source of competition and institution-building. To articulate and test such hypotheses, this article describes two main concepts of government turnover: leadership turnover, or change in rulers, and ideological turnover, or change in the rulers' ideology. Refinements involve the mode, outcome and timing of turnover. The article discusses measurement issues that arise when there are multiple power institutions and when parliaments are controlled by changing majority coalitions. The measures of turnover are illustrated by examining the post-communist world. The article considers the possibility that higher cumulative post-transition turnover - in terms of leaderships or ideologies - has assisted in establishing the rule of law.