The Finnish archaeologist Aarne Michaël Tallgren is remembered for his article on archaeological theory, which he published in Finnish in 1934 and in French for the international readership in 1936. There he denied the possibility of making ethnic conclusions on the basis of archaeological material. However, Tallgren’s relationship to ethnic questions has never before been analysed as a whole. This article examines how Tallgren’s conception of ethnicity developed. He inherited the ethnic paradigm of archaeology from his teachers but was initially rather cautious in his conclusions. Up to 1920, Tallgren’s own approach to ethnic questions gradually consolidated. In contrast to the view prevailing today, it is shown that ethnic conclusions were a central part of his reasoning in the 1920s but only in relation to the question of the roots of the Finnish people. Criticism against the ethnic paradigm of archaeology was voiced both in Finland and elsewhere in Europe in the 1910s and 1920s, and in the early 1930s, Tallgren also began to doubt this approach. Becoming acquainted with the new Soviet archaeology in the late 1920s sparked Tallgren’s interest in archaeology as social history, and the political use of the ethnic view of prehistory first in Germany and soon thereafter in the Soviet Union probably eventually led him to deny any ethnic conclusions.