EYWORDS This paper examines regional, ethnic-specific patterns and Assortative mating; ethnicity; individual-level correlates in same ethnic marriages (endogamy) Indonesia; ethnic and ethnic intermarriages in Indonesia. With data from over 47 intermarriage; development; million couples in prevailing marriages from the full enumeration social change; marriage of the 2010 Census, we outline the provincial variations in endogamy against development indicators and an ethnic fractionalisation index. We compare the prevalence of endogamy for major ethnic groups, and use network plots to examine pairing patterns in ethnic intermarriage. We use multivariate analysis to summarise the relationships between the likelihood of endogamy and migration status, ethnic group size, age group, and education for individuals in two selected provinces: North Sumatra and Jakarta. There is evidence to support negative associations between endogamy rates and provincial development indicators. Endogamy rates vary across major ethnic groups, and as expected, are higher in relatively large ethnic groups. In Jakarta and North Sumatra, individuals in urban areas, with younger age, and higher level of education have lower likelihood of endogamy. We found a positive relationship between ethnic size and endogamy, but conflicting results on the association between lifetime migration and endogamy in both provinces. By studying ethnic pairing patterns, this research provides a unique window to understand the dynamics of development, social change, and social stratification in an ethnically diverse emerging democracy.