Think about the last time you split a dessert with a friend. Did you carefully cut equal slices, or did you grab the bigger piece? Did your friend’s reaction cross your mind before you made your cut? Standard economics once assumed people care only about their own payoff — that we are purely self-interested. This chapter turns that idea around. We explore the evidence that people genuinely care about fairness, equality, and how others treat them. These social motives shape everything from getting along at work to international treaties.