In today’s working life, it has been argued that employees themselves to a large extent are expected to take charge of their own careers. However, some individuals may feel a lack of control over their careers as they feel stuck working in a workplace/organization they do not want to continue to work in, but perceive that they have few if any chances to leave for a better alternative elsewhere. Such a position has been referred to as being locked-in at the workplace. As professional life occupies a large part of the lives of many individuals, it could be argued that being locked-in has negative consequences for the individual. This also means that potential risk factors that lead to a locked-in position need to be identified to prevent such involuntary career non-mobility. However, there is paucity of research on this topic. Consequently, the overall aim of this thesis was to examine the phenomenon of being locked-in in terms of possible determinants related to the individual, and furthermore, consequences for well-being and health. In the present thesis, being locked-in was conceptualized as 1) combining being in a non-preferred workplace/organization with low perceived employability, and 2) adding an additional category including individuals at risk of becoming locked-in. The aim of Study I was to examine determinants of being locked-in. In particular, matching factors between the employee and the work, as well as demographics, were studied. The results indicated that misfit between knowledge/skills and work tasks was related to being locked-in. More specifically, it was revealed that being overqualified or not having enough physical or mental work abilities increased the odds ratios for being or becoming locked-in. Also, both unskilled manual workers and non-manual workers in lower positions were found to have higher odds ratios for being/becoming locked-in. Study II examined the relationship between helplessness and being locked-in, specifically focusing on the cross-lagged relationship between these two factors. The analyses indicated that helplessness worked in both ways, but should primarily be regarded as a determinant of being locked-in. Finally, Study III showed that there were differences in levels of reported depressive symptoms and self-rated health between employees who were stably locked-in compared to employees who were not being locked-in. The ‘risk category’ exhibited an intermediate position, with better well-being and health than those who were locked-in, but with worse well-being and health than those who were not locked-in. Furthermore, a change of locked-in status over time was followed by changes foremost in depressive symptoms. Specifically, positive changes in locked-in status corresponded to positive development, while negative changes in locked-in status were followed by negative development in terms of depressive symptoms and to some extent, self-rated health. In conclusion, this thesis contributes to knowledge of the phenomenon of being locked-in—which is a rather neglected topic in research—by incorporating it into a theoretical perspective of career control and PE fit, as well as by developing its conceptualization/operationalization. Furthermore, this thesis contributes to the research field by examining the relationship between being locked-in and various determinants associated with the individual, and consequences related to health.