Happiness is a kind of subjective feeling of positive emotions. Since the psychological process of reward is closely linked to pleasure, studies to elucidate the brain mechanisms of happiness have focused on the neural circuitry that processes reward information. Brain imaging studies have revealed that the orbitofrontal cortex, cingulate cortex, medial prefrontal cortex, insula, nucleus accumbens, ventral pallidum, substantia nigra, and ventral tegmental area are the key areas related to happiness. When we consider the brain mechanisms of happiness, we need to distinguish between the neural mechanisms for liking and wanting, and between those that encode and cause pleasant feelings. Among these brain areas, subcortical structures participate in “wanting”, while cortical areas participate in “liking”. Orbitofrontal activity has been shown to encode the subjective experience of pleasure. However, it is not clear whether orbitofrontal activity actually causes pleasant feelings. Since the neuroscience of happiness is still in the primitive stage, further experiments are needed to elucidate the brain mechanisms of happiness.