An estimated 14–20 million persons are currently living and working in countries where they are neither citizens nor immigrants. Half of these nonimmigrant workers are legally admitted ‘guestworkers’; the rest are ‘illegal aliens’ or ‘undocumented workers.’ These migrant workers must be distinguished from two other transient groups: the 1 million permanent immigrants who begin anew in another country each year and the 13 million refugees living outside their country of citizenship and liable to prosecution if they return. The distinctions between the three groups are often blurred, as when migrant workers become immigrants.

The migration familiar to Americans moved transients and settlers from East to West. The migratory chain established in the nineteenth century recurs today – single males migrate first and later are joined by their dependents. Family reunification and formation establish a community in the receiving area to which later migrants come. Thus is forged the migratory chain which moves people between two areas. From 1800 to 1920, some 50 million Europeans arrived in the Americas. Early waves of immigrants intended (or were forced) to effect a relatively clean break with their homeland.

Migration streams mature over time. The second wave of immigrants in the late nineteenth and early twentieth centuries contained many ‘target earners’; young men who hoped to work hard, live frugally, save money, and return home to marry, buy a farm, build a house, or open a small store.