Joy, sorrow, jealousy, and awe—these and other feelings are the stuff of our daily lives. In the seventeenth century, the philosopher Spinoza devoted much of his life's work examining how these emotions supported human survival, yet hundreds of years later the biological roots of what we feel remain a mystery. Leading neuroscientist Antonio Damasio—whose earlier books explore rational behavior and the notion of the self—rediscovers a man whose work ran counter to all the thinking of his day, pairing Spinoza's insights with his own innovative scientific research to help us understand what we're made of, and what we're here for.