While existing research has demonstrated that intrinsic motivation can increase task performance, jobs are composed of multiple tasks, and it remains to be seen how intrinsic motivation in one task affects performance on other tasks. Drawing on theories of psychological contrast, we hypothesize that high intrinsic motivation in one task reduces performance on less intrinsically motivating tasks. In a field study at a Korean department store, employees with the highest maximum intrinsic motivation in one task had lower average and minimum performance across their other tasks as well as more performance variance across their tasks. In a laboratory experiment in the United States, working on a highly intrinsically motivating initial task led participants to perform worse in a subsequent task if it was uninteresting, but not if it was interesting. This effect was mediated by boredom, but not by a range of other psychological processes. Across both studies, moderate intrinsic motivation in one task was associated with better performance in less interesting tasks than high intrinsic motivation, revealing a curvilinear cross-task effect of intrinsic motivation. Our research advances knowledge about the dark side of intrinsic motivation, the design of work, and the drivers of task performance. Copyright of the Academy of Management, all rights reserved. Contents may not be copied, emailed, posted to a listserv, or otherwise transmitted without the copyright holder's express written permission. Users may print, download, or email articles for individual use only. motivation. When the first task was highly intrinsically motivating, they performed worse on a second task if it was uninteresting, but not if it was interesting. This effect was mediated by boredom, but not by alternative emotions of anger, anxiety, sadness, disgust, relaxation, happiness, desire, or humor-and was also not explained by cognitive processes of depletion, attention residue, or perceptions of task complexity, difficulty, and cognitive load. Across the two studies, moderate intrinsic motivation yielded better performance on less interesting tasks than low or high intrinsic motivation, yielding an inverted U-shaped cross-task effect of intrinsic motivation. Our research extends knowledge about work motivation, design, and performance in three key ways. First, in contrast to the dominant emphasis on the performance benefits of intrinsic motivation, we document that it can be a double-edged sword. The evidence that intrinsic motivation can reduce cross-task performance addresses calls to systematically study how there can be too much of a good thing (Grant & Schwartz, 2011; Pierce & Aguinis, 2013). Second, when an employee excels in one task but struggles in another despite possessing the requisite skills to succeed in both, this discrepancy is often attributed to the fact that the first task is motivating while the second task is not (e.g., Ashford & Northcraft, 2003; MacKinnon, 1962; Schmidt & DeShon, 2007). Our studies highlight the complementary pos...