The coca leaf has played an important role in the lives of South American Indians for thousands of years. Its use as a masticatory persists today in many parts of the Andes, from northern Colombia, south to Bolivia and Argentina, and in the western part of the Amazon Basin. Coca leaf is used as a mild stimulant and as sustenance for working under harsh environmen­tal conditions by both Indians and mestizos alike. It also serves as a univer­sal and effective household remedy for a wide range of medical complaints. Traditionally, coca also plays a crucial symbolic and religious role in An­dean society. The unifying and stabilizing effects of coca chewing on An­dean culture contrasts markedly with the disruptive and convoluted phenomenon of cocaine use in Western societies. Because all cocaine enter­ing world markets is derived from coca leaves produced in South America, the staggering increase in demand for cocaine for recreational use has had a devastating impact on South American economies, politics and, most tragically, on indigenous cultures. The widespread intranasal use of cocaine hydrochloride or smoking of cocaine base produce quite different psychological and pharmacological ex­periences than the traditional chewing of coca leaves. The differences be­tween taking concentrated cocaine and chewing coca have been pointed out repeatedly by earlier workers (Mortimer 1901; Weil 1975; Grinspoon and Bakalar 1976; Antonil 1978; inter alia). Yet many people still equate the use of coca with that of cocaine and fail to comprehend either the pharmacological or cultural differences between these two related, though unique, substances. In Western society, the public is well aware of both the pleasurable and deleterious effects of cocaine because of extensive news coverage of the cocaine "phenomenon" of recent years. Few people, however, are aware of the beneficial effects of coca chewing, of the impor­tance of the use of coca in Andean life, or of the origin and evolution of the coca plant. The purposes of this paper are twofold: first, to describe the process of coca chewing, the effects of coca and how it is used traditionally; and sec­ond, to discuss the botanical sources, antiquity, geographic distribution and putative evolutionary history of coca. Most of the information presented here has been published elsewhere and recently summarized (Plowman 1984a, 1984b). Readers are directed to these articles for more detailed infor­mation and references.