Social norms are informal rules of behavior that individuals follow because they think others also follow them, think they should be followed, and are willing to sanction those who deviate. They affect a number of outcomes of interest to political scientists, both at the citizen and at the elite level. Because they rest on the anticipation of sanctions, norms can bring about mismatches between the private and revealed preferences of individuals. Since norm change represents a coordination problem, even unpopular norms can persist for long. For them to change, individuals need to update their priors as to what others deem acceptable. In the realm of politics, such updates can be brought about by institutional signals, information shocks from elections, or elite rhetoric.