This article argues for the need to differentiate between "professional" and "support" careers in fields of science, technology, engineering, mathematics, and medicine (STEMM). Using data from the Longitudinal Study of American Youth (LSAY), the article identifies important differences in the nature of the work and responsibility that differentiate the scientific workforce into a professional component and a support component. Further analysis demonstrates that the kind of training and education needed for STEMM support occupations is generally lower and different than the education needed for entrance into a STEMM profession. The LSAY data indicate that the students planning to enter a STEMM profession tend to make their choice earlier, select appropriate courses and programs to obtain professional credentials, and make a substantially longer commitment to educational preparation than do young adults who enter STEMM support occupations. We suggest some policy implications that may flow from this distinction. (Contains 2 tables.)