Based on four individual studies, the present thesis investigates the effects of economic (extrinsic incentives) and social determinants (peer effects and worker heterogeneity) on workers effort choice decisions and, thus, worker productivity. Following a general introduction to personnel economics, the first study addresses the ambivalent effects of work group diversity on worker productivity by means of a meta-analysis. Results suggest negative population correlations of gender and age heterogeneity on team performance and positive correlations of educational background diversity. Moderator analyses of team size and team type are included. The subsequent three studies build on insider econometric data on worker productivity derived from within a large European automobile manufacturer. The second study analyzes potential social (e.g. work unit size, turnover) and economic (e.g. prosperity level) influences on employee absenteeism in the international context. Findings reveal significant context and plant related effects. The third study analyzes employees behavioral responses to the abolition of an existing incentive system. Results imply that employees intrinsic and social motives are crowded-out by monetary rewards and, therefore, overall performance is significantly lower when extrinsically incentivized. Finally, the fourth study investigates the performance behavior of employees who are promoted from temporary to permanent contracts. Findings suggest about half of the employees to significantly reduce performance when having signed a permanent contract. Eventually, the results of all four studies are summarized and general economic insights/conclusions are suggested.