Nursing's attention to cultural diversity has been influenced by the changing demographic composition of the U.S. population. Nursing must continue to increase awareness and promote attitudinal and behavioral changes that will result in the delivery of culturally appropriate nursing care. The nursing literature includes several models of cultural development to assist nurses and other health care professionals in conducting a cultural assessment and incorporating cultural data into nursing care plans. This article presents a synthesis model of cultural development that illustrates that cultural awareness, cultural sensitivity, and cultural competence do not achieve the level of cultural development necessary to meet the health care needs of a diverse population. Cultural proficiency is a concept that extends cultural competence into nursing practice, administration, education, and research. It is a philosophical and behavioral approach to cultural diversity that guides and prescribes individual and institutional behavior toward "cultural others."