A veritable boom in immigration research has taken place in the last 15 years. The purpose of this article is to provide a conceptual map, a way of presenting the issues and approaches that pertain to the topic, to guide us through the vast territory immigration research now encompasses. As this boundless growth in immigration research has occurred across the social sciences, this review of the literature is not intended to be exhaustive but merely illustrative of what sociologists, historians, and anthropologists have contributed. Since America is the quintessentially immigrant society, the focus is on American immigration, but the theoretical issues this review highlights can be applied equally well to other societies with histories of immigration and racial or ethnic relations, such as Great Britain or Brazil. Increasingly, immigration research is one of the topics where sociologists and historians meet (research on revolutions is another), although they meet in much the same fashion that one sometimes arrives at a party and is much surprised to find out who else is there. Our common research interests increasingly bring us together, although not without a fair amount of surprise and trepidation.