A study of Costa Rica can help assess the usefulness of office-seeking, sociological, and institutionalist approaches in explaining why parties reform electoral laws. In line with office-seeking theories, reelection incentives discouraged most Costa Rican presidents and legislators from supporting reforms that threatened their electoral performance. However, as sociological theories suggest, some politicians endorsed major reforms because they came from outside traditional party networks. Nevertheless, in line with institutionalist theories, they succeeded in assembling coalitions to pass reforms only when the larger parties had equal access to patronage and power, Only the additional pressure of public opinion and, most important, civil war enabled presidents to build legislative support for electoral reform.