Why do candidates make ethnic appeals in election campaigns? More specifically, why do some candidates appeal to their ethnic group while others reach out to different ethnic groups or abandon ethnic appeals altogether? This book develops key concepts of ethnic bonding, bridging, and bypassing to interpret ethnic politics in Indonesia, one of the world’s largest and most ethnically diverse emerging democracies. Examining local and national elections over two decades, it draws on a content analysis of religious and indigenous appeals coded from newspaper election reports and over 25,000 election posters. Findings show that three core factors—electoral rules, party ideology, and ethnic group viability—interacted to guide candidates’ ethnic appeals. Under party-centric electoral rules, candidates’ bonding, bridging, or bypassing strategies were shaped by their party’s ethnic or nonethnic ideological stance. Under candidate-centric rules, candidates disregarded party ideology. Instead, they sought out and appealed to any viable co-ethnic groups within their constituency. To be viable, a group had to be large enough to enable electoral victory and there had to be no social norms restricting candidates from appealing to that group. In the absence of a viable ethnic group, candidates turned to bridging or bypassing strategies. The book goes beyond the standard view that the politicization of ethnicity is problematic by specifying the microfoundations for candidates’ ethnic appeals. It allows us to predict which ethnic identities will become politicized in future elections and provides prescriptions on how to curb divisive ethnic politics.