We investigated intentional thinking for pleasure, defined as the deliberate attempt to have pleasant thoughts while disengaged from the external world. We propose a Trade-Off Model that explains when and why thinking for pleasure is enjoyable: people focus on personally meaningful thoughts when thinking for pleasure (especially when prompted to do so), which increases their enjoyment, but they find it difficult to concentrate on their thoughts, which decreases their enjoyment. Thus, the net enjoyment of thinking for pleasure is a trade-off between its benefits (personal meaningfulness) and costs (difficulty concentrating). To test the model, we compared intentional thinking for pleasure to four alternate activities in three studies. Thinking for pleasure was more enjoyable than undirected thinking (Study 1) and planning (Study 3), because it was more meaningful than these activities while requiring a similar level of concentration. Thinking for pleasure was just as enjoyable as playing a video game (Study 2) or unprompted idle time activities (Study 3), but for different reasons: It was more meaningful than these activities, but required more concentration. We discuss the implications of these findings for what people might choose to do during idle times.