Book excerpt: Deals with the two great migration waves: from 1820 to the outbreak of World War I, when immigration was nearly unrestricted; since 1950, when mass migration continued to grow despite policy restrictions. Covers north-north and south-north migration, i.e. to the New World and contemporary Europe, as well as south-south migration. Assesses the impact on the migrants themselves, and repercussions on the sending and receiving countries.