Moonlighting workers represent a significant percentage of the labor force. The motives for moonlighting include the inability to work sufficient hours or earn enough money on the primary job, as well as a desire for a nonpecuniary aspect of the second job that is unavailable on the primary job. We refer to these motives as primary job constraints and heterogeneous jobs. We present extensive descriptive and econometric evidence using the SIPP, and conclude that both general motives are important