Previous research on the relation between affect and worker productivity has generally shown mixed results. While many studies find that happy workers are more productive, others show no relation. The current paper suggests that the relation between happiness and productivity may vary depending on how happiness and productivity are operationalized. It is proposed that happy workers may be better at certain tasks (e.g. tasks that require creativity or helpfulness), while less happy workers may be better at other tasks (e.g. tasks that require detail orientation or competition) and that this may account for the mixed past findings. Two studies were conducted to examine the effect of positive and negative affect on task performance. Study 1 examined the relation between employee trait affect and performance ratings by supervisors in a variety of different jobs. It was found that affect predicted performance differentially depending on the area of performance that is being measured. It was also found that the types of tasks performed on the job moderated the relation between affect and job performance. Study 2 utilized a student sample to examine the hypothesized mechanisms underlying these relations using structural equation modeling.