Researchers have documented various (sometimes conflicting) effects of music on cognitive task performance, and have highlighted several mechanisms through which these effects may occur (e.g., arousal, mood, attention). To further understand these effects, we consider interactions between musicbased, task-based, and performer-based characteristics. Specifically, we drew from the distractionconflict theory of social facilitation and research on boredom proneness to hypothesize that music-along with its complexity and volume-facilitates simple task performance and impairs complex task performance, and that one's preference for external stimulation (a dimension of boredom proneness) moderates these effects. We tested our hypotheses in a laboratory experiment, in which participants completed cognitive tasks either in silence or with music of varying complexity and volume. We found that (a) music generally impaired complex task performance, (b) complex music facilitated simple task performance, and (c) preference for external stimulation moderated these effects. Therefore, the data suggest that music's effects on task performance depend on the music, the task, and the performer. Public Significance Statement In this study, we found that music generally impaired performance on a complex task, whereas complex music improved performance on a simple task. These effects depended on the task performer's personality, suggesting the need to consider music-, person-, and task-based factors when deciding whether to integrate music into work environments.