An integrative theory about mood and motivation—the mood-behavior-model (MBM) (Gendolla, 2000)—is presented and the results of related studies on mood and motivational intensity are discussed. A series of experiments with implications for motivation in organizational and educational settings assessed motivational intensity as cardiovascular reactivity in the context of task performance. The results support the theoretical predictions and demonstrate that (1) moods do not per se have an effort mobilizing function, (2) moods are pragmatically used as information for demand appraisals, (3) mood congruent demand appraisals determine effort-related cardiovascular response, (4) performance-contingent incentive determines the level of maximally justified effort, (5) effort is linked to achievement. The findings specify and extend other approaches to the role of affect in motivation and have direct implications for clinical psychology, work psychology, and health psychology.