Students often sign up for introductory anthropology courses in order to learn more about human groups that they see as fundamentally different from them. But further acquaintance with the discipline leads to the discovery that some of the most fascinating problems center on the attempt to define what human beings every where have in common. Documenting human differences, whether biological or cultural, was at one time a major concern of anthropology. Explaining these differences, along with those conditions that humans share in common, is another matter. The major efforts in anthropology today are addressed to explanation, and it is this concern that informs our text. Although ample descriptive material is provided to give students a clear understanding of the information with which anthropologists deal, this text stresses of processes of interaction and change, not only among different human social groups but also between these groups and ecosystems in which they live.