The public controversy which developed between 1896 and 1920 in the Canadian prairie provinces over the question of immigration is examined in this paper. It is shown that although many of the social, political, religious and cultural characteristics which have differentiated the prairies have been a result of ethnic diversity, the predominantly white Anglo-Saxon Protestant population which pioneered the prairies was initially resistent to many immigrant groups. The non-restrictive immigration policy, developed by Minister of the Interior Sifton to stimulate agricultural and economic growth of the region, and its social, political, and economic effects are considered in detail. Acceptance or rejection of various groups (Asians, Central and Eastern Europeans, blacks) and their subsequent assimilation processes (particularly with regard to language) are explained. The issues of racism, social reform, feminism, radicalism, prohibition and naturalization are described in light of the changing social situation and the prevailing political and intellectual currents. Attitudes towards assimilation and immigration legislation are detailed for each ethnic group and, finally, effects of the immigration process on various groups up to 1970 are summarized. (WI)