The paper analyzes the determinants of part-time employment, mini- and midi-jobs in Germany. Theory implies that all three employment types could be used as instruments of flexibility to react flexibly to demand shocks. But the empirical analysis shows that only mini- and midi-jobs are significantly correlated with the demand shock and that they are used as working time flexibility instead of a peripheral workforce. A restraint for working hours reductions are quasi-fixed employment costs so that firms with a higher share of qualified employees in their workforce make less use of such a reduction. Overall the empirical findings suggest that working time preferences of the employees are a key factor. Furthermore, mini- and midi-jobs are used more likely and intense if there are no representations of employees interests