The purpose of this study is to provide a systematic and quantitative review of the existing empirical evidence on the effects of unionization on overall job satisfaction. We conducted a meta-regression analysis (MRA) with results from a pool of 235 estimates from 59 studies published between 1978 and 2015. The accumulated evidence indicates that unionization is negatively related to job satisfaction but is far from being conclusive. When primary studies control for endogeneity of union membership, the results of the MRA indicate that the difference in job satisfaction between unionized and non-unionized workers disappears. These results suggest that reverse causation (i.e. dissatisfied workers are more likely to join a union) and time-varying endogenous effects play a key role in explaining the relationship between unionization and job satisfaction.