Medicine has become interested in unconventional healing practices, ostensibly because of recent demographic research that reveals a thriving medical market of multiple options. This essay presents a historical overview of medical pluralism in the United States. Consistent evidence is examined suggesting that unconventional medicine has been a persistent presence in U.S. health care. Despite parallels with the past, the recent widespread interest in alternative medicine also represents a dramatic reconfiguration of medical pluralism-from historical antagonism to what might arguably be described as a topical acknowledgment of postmodern medical diversity. This recent shift may have less to do with acknowledging "new" survey data than with representing shifts in medicine's institutional authority in a consumer-driven health care environment. This essay is an introduction to a discussion of a taxonomy of contemporary U.S. medical pluralism, which also appears in this issue.