The overall address of the present thesis is the association between being 'on fire' and burnout. More specifically, the thesis focused largely on two representations of involvement in work (work engagement and Type A behavior) and their respective relationships to burnout. Another pervasive theme was construct validity in assessing burnout and work engagement. These themes were addressed in four empirical studies, conducted in a sample of healthcare workers (Study I) and a sample of information communication technology consultants (Studies II, III, and IV). Study I aimed to extend the previously preliminary support for the construct validity of the Swedish version of the Maslach Burnout Inventory (MBI). The objective of Study II was the discriminant validity of the Utrecht Work engagement Scale (UWES) against the theoretically adjacent constructs of job involvement and organizational commitment. Another objective was the translation and evaluation of a Swedish version of the UWES. In Study III, the aim was to investigate the (cross-sectional) association between Type A behavior, work engagement and burnout. Study III had two foci: 1) whether global Type A behavior interacts with job factors to affect burnout and work engagement, and 2) the associations between the main components of Type A behavior (achievement-striving and irritability/impatience) and burnout as well as work engagement. Study IV concerned the longitudinal relationships between Type A behavior and burnout, and between work engagement and burnout. The results presented in this dissertation support the construct validity of Swedish versions of the MBI and UWES. It was further indicated that emotional exhaustion and depersonalization (or cynicism) constitute the core aspects of burnout, and that work engagement was more prominently associated with lack of health complaints than job involvement and organizational commitment. Global Type A behavior was positively related to work engagement in cross-sectional data but unrelated to burnout. When the dimensionality of Type A behavior was taken into account, it was indicated that the achievement-striving aspect of Type A behavior that was associated with work engagement, whereas irritability was associated with less engagement and more burnout complaints. No indications of an interaction between (global or the sub-dimensions of) Type A behavior and job stress were found. The most important finding of Study IV was that change in Type A behavior was unrelated to change in burnout across time (one-year interval). Furthermore, Study IV supported the notion that work engagement and burnout are bipolar opposites in a work well-being continuum. To conclude, the present thesis suggests that burnout be viewed as an erosion of intrinsic, affective engagement in work, occurring when intrinsic motivation is frustrated by job stress. To avoid conceptual confusion, burnout should be distinguished form exhaustion syndrome, however it should be acknowledged that burnout may have a negative impact on health. The...