From the perspective of the sociology of language developed by Joshua Fishman, and working from letters, newspapers, secondary accounts, and grave inscriptions, this study describes and explains bilingualism and the loss of the Dutch language in two West Michigan Dutch immigrant communities from 1847-1930, the Reformed Church (RCA) Dutch and the Christian Reformed Church (CRC) Dutch. The loss of Dutch in some ways parallels the contemporaneous language shift of Norwegian immigrants (Haugen, 1969) and Swedish immigrants (Karstadt, 2002). The two West Michigan Dutch Calvinist communities were unique in their language shift experiences. The RCA Dutch experienced and promoted a rapid assimilation and shift to English. The CRC Dutch promoted a multi-generational maintenance of the Dutch language in a stable Dutch- English bilingual setting-the preservation of Dutch was not at the expense of the acquisition of English-and then consciously and abruptly abandoned the Dutch language in the years immediately after World War I. The CRC Dutch maintained their language for so long precisely because it was the marker of identity for them and it was inextricably tied to their faith; the RCA Dutch were able to abandon the Dutch language early on because it was not the marker of religious identity for them.