An exemplary study of a very important problem. Far from limiting himself to a purely statistical study of human migration across the border, the author has approached the problem rather from the angle of cultural relations, stressing the difficulties of the unskilled Mexican laborer in a country where he finds a different mentality, language, social organization and frequently religion. The writer feels that migration of a temporary nature, which supplies this country with unskilled labor, is not to be deprecated, but insists that some effort should be made to restrict permanent immigration, for the good of both countries. Señor Gamio has had a thorough sociological education, has been sub-secretary of education in Mexico and holds high office in the Mexican Government. He speaks with authority, and his book should help to attract attention in this country to an important but neglected problem.