Research suggests public policy influences social norms, but little is known about how this process takes place. This study contributes toward diminishing this gap, by illustrating how a national smoking ban strengthened social norms related to no smoking in public places among college students (N = 204). Social norms were conceptualized using an integrative framework of social influence that intersected the nature of social norms (descriptive and injunctive) with sources of influence (sociocultural, subjective, and in-group) and were collected cross-sectionally in time. Social norms regarding being quiet in a library were simultaneously collected to control for variations between subjects. The research design was 2 (content of norms: no smoking in public places vs. being silent in a library) × 3 (time: 1 month before vs. 6 months after vs. 1 year after the ban). As expected, only social norms toward no smoking in public places changed throughout time. Descriptive and injunctive norms with sociocultural and subjective agents increased, especially after 6 months had gone by. Smoking status effects were analyzed but, unexpectedly, no interaction with time was found. Results imply that the ban triggered specific types of social norms and, therefore, public policy might benefit from further understanding these effects.