This grounded theory research explored the basic social processes of how nurses develop and evolve their value systems. Multiple data was gathered from 54 Indonesian nurses across a range of clincial settings, including focus group and individual interviews, anecdotal and reflective stories. Data analysis informed the construction of the theory, Becoming a nurse: Developing and evolving a value system (the DEVS theory). The theory deepens our understandings of how nurses establish, negotiate and manage personal-professional values whilst navigating through their challenging professional life. Education strategies are recommended to enhance awareness of personal-professional values negotiation in nursing practice.