Norms indicate which behaviors are common and/or considered morally right. They may differ across space and time. I show that social-Kantian preferences can explain this. These preferences incorporate two hitherto neglected factors: Kantian moral concerns – which drive personal moral norms and motivate unconditional following thereof – and attitudes towards making a different material sacrifice than others –which motivate conditioning own on others’ behavior. Conditions on preference and belief distributions promoting/hampering spontaneous changes in the behavioral norm (the modal behavior) are identified. Implications for policy interventions aimed at changing norms, and key differences with commonly used models are discussed.