Since the end of World War II, the Guam native population, who are mostly Roman Catholics, has undergone one of the most dramatic socioeconomic developments ever recorded. They have rapidly become incorporated into the dominant American culture and economy. This accelerated process of modernization has been accompanied by a very sharp fertility decline. One reason for this decline has been the increasing defection of Guam Roman Catholic women from the traditional teaching of their Church on the subject of birth control. This trend of fertility decline, although at higher levels, resembles that of East Asian countries with rapid fertility decline.