Despite Brazil's electoral laws, which would appear to encourage incumbency, legislative turnover in Brazil consistently exceeds 50% with each election. In this article, I explain this phenomenon as a function of two factors: the nature of political ambition and the dynamics of electoral competition. Political ambition accounts for about half of the turnover because a sizeable portion of incumbent legislators decides to run for nonlegislative office. Electoral competition accounts for the other half. Since many potentially strong candidates for reelection decide to run for another office the group of incumbents running for reelection is relatively weak. In addition, a wide-open nomination process ensures that incumbents running for reelection face a pool of extremely strong challengers. Finally, Brazil's at-large, open-list proportional representation electoral system undermines incumbents' attempts to protect their status. Given these factors, many incumbents lose. I provide evidence for the impact of ambition and competition on legislative turnover in Brazil, place Brazil in comparative perspective, and suggest avenues for further research.