This chapter reviews the psychology of self-regulation, highlighting the importance of self-regulation for wellbeing and optimal functioning, how it operates, why it fails, the consequences of its ¬failure and how we can strengthen it. Self-regulation can manifest in different forms, including impulse control, the delay of gratification, controlling thoughts and emotions, behavioural control, performance regulation, making decisions and choices, and habit forming or breaking. Ample experimental research has shown that self-regulation capacities can improve with exercises that require consistent applications of self-control, similar to the ways in which a muscle can be strengthened with regular physical activity. An important aspect of self-regulation that directly impacts people performance and wellbeing is impulse control. Grit requires working persistently to achieve people long-term goals, maintaining engagement and exerting effort consistently over long periods, despite obstacles, plateaus and even in the face of failure.