The anthropological study of medicinal botany has numerous objectives, one of which is to identify ethnomedically important species that warrant chemical analysis and testing for biological activity. This chapter suggests that intra- and intergroup similarities in the use of medicinal plants have arisen and persist because particular remedies produce reactions that are both predictable and considered to be desirable. It argues that ethnomedical systems contain an anticipated, and perhaps even predictable, level of variation in the use of available remedies. Anthropologists and other researchers have used a variety of approaches to identify potentially effective plant based remedies. However, most of these approaches necessitate investigations that range over broad geographic regions, through extensive periods of time, or across multiple cultures. Patterning in the use of medicinal plants, whether seen among Mexican Americans or other societies, reflects a fundamental human condition—adaptation to a complex web of socioenvironmeiital challenges including, of course, sickness and the maintenance of health.