Summary: Having a song stuck in your head is a commonly experienced intrusive thought. We explored the intrusive song phenomenon through a survey, an experimental diary study, and three laboratory experiments. Contrary to the belief that only obnoxious songs get stuck, we found that songs people know and like frequently became intrusive. We also found that intrusive songs followed environmental cues. In addition, if a song continued to play in someone's head immediately after listening to it, the song was likely to return as an intrusive song within the next 24 hours. Similar to mind wandering, the return of intrusive songs depended on cognitive resources: people reported that intrusive songs returned during low cognitive load activities, and we found that overloading the cognitive systems with challenging activities increased intrusive song frequency. Throughout our studies, we easily created and manipulated intrusive song experiences. Songs provide a valuable method to investigate intrusive thoughts. Copyright © 2012 John Wiley & Sons, Ltd.