This chapter explains what happiness is and then document its benefits. It discusses how and why people have trouble predicting and creating their own happiness. The chapter explores the causes of happiness, including research that supports the idea of a genetic predisposition to experiencing happiness with oneself and the world, with one's life circumstances, and with details of one's daily activities. Mindfulness is behavior that can increase level of happiness. The chapter endorses Lyubomirsky, King, and Diener's claim that a person's self-report of happiness is derived from the extent to which he or she experiences positive emotions in everyday life. Most people intuitively connect happiness to the idea of optimism, which is defined by generalized positive expectations for the future. Usually optimism is thought of as dispositional—that is, something that characterizes a person in a habitual way. Similar to happiness, it appears to be associated in a causal way with positive outcomes.