This paper analyzes the determinants of secondary jobholding in Germany and the UK. Although differing in labor market regulations, moonlighting is a persistent phenomenon in both countries. Using panel data from the BHPS and the SOEP, reduced form participation equations are estimated for male and female workers separately. While the results vary across gender and countries, there is support for both main theoretical strands, i.e. the ‘hours-constraints’ motive as well as the ‘heterogeneous-jobs’ motive. In particular, there is evidence that particularly German workers who would like to work more hours are more likely to have a second job. On the other hand, the prospect of starting a new job is associated with moonlighting behavior of mainly British workers.