In this chapter, the author examines the different theories anthropologists have offered to explain the difference in medical systems found in various cultures. One school of thought suggests that medical systems, like cultures in general, largely develop in response to the physical environment. In contrast, others argue that medical systems, also like cultures, are mental constructs constrained little by the physical environment – rather, they hold that one makes the world around him. Hahn ultimately rejects both theories and argues for a theory between the two extremes.