Two decades of turnover data were collected for the national legislature of twenty-five industrialized countries. After a discussion of turnover's significance, we compare turnover rates across countries. A set of variables expected to influence turnover rates is described and multiple regression is used to test the hypotheses developed. Results show that frequency of elections, opportunity for double listings, electoral volatility and legislative institutionalization have statistically significant effects on turnover. In addition the type of electoral system (majoritarian versus proportional representation) is shown to have a statistically and substantively significant effect, with turnover much greater in the latter. Possible explanations for this effect are explored.