The article considers the adaptation of ethnic migrants to new living conditions in the late 19^th and early 20^th centuries in Siberian society: what strategies were chosen and what institutions of self-organization were created to help immigrants adapt. In the last quarter of the nineteenth and early twentieth centuries Eastern areas of Russia became a place of attraction for mass migration flows having voluntary and forced nature. Both peasants and city dwellers, representatives of different social strata, classes, confessions, and ethnicities, started resettling. The need to adapt to new living conditions and to get integrated into the Siberian society made group consolidation and diaspora-oriented strategies of adaptation necessary. The success of group adaptation strategies for Germans and Jews was due to the fact that living in diaspora had been the norm for them even before resettling to Siberia. People descending from the Baltic States, the Kingdom of Poland or the Western region (Poles, Ukrainians, Estonians, and Latvians) acquired their own and yet new for them experience in building their diasporas in Siberia. Cross-border migrants – the Koreans and the Chinese – demonstrated their own models of group self-organization. A necessary element of diaspora building in migrant communities was the creation of specific social institutions capable ensuring successful and painless adaptation to new living conditions without losing religious or ethnic identity. Originally, diasporas were built on religious basis. Lutheran communities included Germans, Latvians, and Estonians Catholic communities attracted Poles, Belarusians, and Germans Muslim communities incorporated mainly the Tatars (Siberian ones as well as newcomers). It was only the Jewish community that remained ethnically homogeneous, bringing together the Jews. These processes occurred in the context of an estate society in which religious institutions were a part of basic ground. Therefore, the authorities considered self-organization of migrants within religious communities as necessary and legitimate. However, with the decay of the estate system by the early twentieth century, elements of a new social structure “matured” in its core. Part of this process was the formation of ethnic identity. Along with religious social institutions there were created secular ethno-cultural organizations language, secular national school, and the idea of common historical destiny all gained significance. Building Diasporas in the Siberian resettlement society acquired ethnic overtones. Religious identity was replaced by ethnic one. Institutionalization of ethnicity took place and religious communities were replaced by ethnic ones. Decisive role in the transformation of religious identity into ethnic one was played by the emerging secular elite (national intelligentsia).