A four-round Delphi technique was conducted on 127 experienced Japanese nurses to develop a consensus of opinion on the defining characteristics underlying expertise, and the prime requirements for the development of expertise in clinical nursing. Sixteen statements identified as the prime defining characteristics underlying expertise indicated that experienced Japanese nurses' picture of expertise is general, comprehensive and focused on task expertise. Four prime requirements for the development of expertise identified indicated that neither experience nor accumulation of theoretical knowledge alone is sufficient to develop expertise; but that motivation and attitude do play an essential role in the development of expertise.