Ethnic party electoral success follows the same general principles that apply to all political parties, with electoral rule, group size and territorial concentration key factors, but there are some important differences. Ethnic groups may choose to form one or more ethnic parties or they may choose to seek influence within a mainstream party; and ethnic groups may benefit from special quota rules. We show that, worldwide. only a third of the ethnic groups that are large enough and territorially concentrated enough to form parties do so, and that ethnic groups that are not geographically concentrated and which must operate without special ethnic quotas have very close to a zero probability of forming an ethnic party that succeeds in gaining representation. However, patternsdo differ by region, especially with respect to whether special ethnic party rules are in place.