In the last few years, a growing number of studies have reported strong interplay between Work-Life-Imbalance and health complaints. Negative spillover from work into private life has often been found to be a mediator between work characteristics and health complaints. No adequate German instrument to measure relations between work and private life was available. Therefore, the first part of this thesis presents the development and successful validation of a questionnaire that measures negative spillover between work and private life in both directions. In the second part of this thesis it will be examined whether the mediator role of negative spillover can also be found when work characteristics (job demands and job control) are measured independently of job incumbents, i.e., when self-reported bias can be ruled out as a likely alternative explanation of the findings. The results demonstrate that the peviously reported relations between job characteristics, negative spillover, and vital exhaustion are not merely a consequence of biased subjective perception, but are rooted in the ‘‘real’’ job environment. However, whereas expert-rated job demands have an impact on negative spillover and vital exhaustion without being perceived, the perception of job control plays a crucial role for the relations between expert-rated job control, negative spillover, and vital exhaustion, but not for Major Depression.