This article aims to bridge the circadian and self-control literatures by suggesting that people's self-control performance varies as a function of their circadian preferences (i.e., chronotype). We review evidence for this assertion across a wide range of self-control domains, including cognitive processing, emotion regulation, interpersonal relationships, and social inf luence. Across these widely ranging behaviors, the results indicate that when people's circadian preference matches the time of day, a synchrony effect occurs, and self-control performance is at its peak. Therefore, people are more likely to display self-regulatory failures and give in to temptations when there is a mismatch between their circadian preferences and time of day. Overall, this article offers new insights into the relationship between circadian preferences and self-control and suggests novel and exciting new directions for future research.They are angels or demons just as they are fresh or tired. (William James, 1890) Imagine two individuals awaking to their 6 AM morning alarm. The first individual wakes up alert, eats a healthy breakfast, squeezes in a yoga session, and then arrives to work 10 min early. The second individual hits the snooze several times before rolling out of bed, skips breakfast, grabs an extra-large coffee on the way to work, and arrives 10 min late. Now, fast forward to the end of their day. Our alert morning person is now spent from the day's work. Too tired to cook, she grabs some fast food on the way home. However, our groggy morning person is ready to tackle the night. She joins a few friends at the gym and then heads home to cook a healthy post-workout meal. If both of our individuals had the same amount of sleep the night before, what causes their variations in behavior? The answer lies in an individual's circadian rhythm preference.Circadian rhythm preference, or chronotype, refers to a person's variation in sleep/wake and alertness patterns (Adan et al., 2012;Schmidt, Collette, Cajochen, & Peigneux, 2007). Morning-type (MT) people go to bed and wake earlier and feel more alert and energized in the morning. Evening-type (ET) people go to bed and wake late and feel more alert and energized in the evening. The present article examines how such preferences inf luence people's ability to exert self-control and resist temptations throughout the day. As our opening example suggests, morning people should be better equipped to exert self-control in the morning, whereas evening people should be better equipped in the evening. As the James quote above suggests, if people encounter temptations during their non-preferred time of day, they will be less likely to resist and will therefore engage in undesirable behaviors.In this article, we brief ly review the circadian rhythm preference literature. We then brief ly review self-control literature. Next, we attempt to bridge these two disparate literatures by reviewing research that suggests successful self-control varies throughout the day as a function of circadian i...