All professions have practitioners who are considered to be experts. Less is known, however, about how these people achieve this level of excellence and about the factors that influence the attainment of expert practice in any profession. Using acknowledged expert nurses as a focus, this dissertation explored and evaluated the following factors that the literature suggested affect the progression from novice to expert: information-processing, problem-solving, and intuition abilities: mentors and mentoring: motivation and education: experience: and institutional incentives. An additional factor -- intrinsic motivation, which was not identified a priori, emerged in the course of the research. The conceptual framework used for this study was the novice-to-expert progression developed by Dreyfus & Dreyfus and applied to nursing by Benner. Benner's framework comprises novice, advanced beginner, competent, proficient, and expert. A qualitative case study method was used employing in interviews of ten clinical nurse specialists (CNSs). Data analysis was conducted following standard procedures for qualitative descriptive analysis. The study demonstrated that all of the CNSs progressed through each of Benner's stages during their careers. The following factors were identified as influential in their achieving expertise: information-processing and problem solving; mentors and mentoring; motivation and education; experience; intrinsic motivation. Institutional incentives and intuition played very weak roles and were not considered influential in achieving expertise, although the CNSs stated that the latter was an important element of their practice. This study has several implications for practice and research. With respect to practice, there is a clear need for mentoring programs, graduate education, internship programs, a stronger emphasis on experience, and policies to assure patient assignments are correlated with the level of the practitioner. Further research is suggested on all factors identified, especially the clinical ladder. The study contributes to adult education theory by clarifying the factors which foster the attainment of expertness, and to practice by suggesting areas in which interventions and innovation might be effective. / Ph. D.