The behaviors and expectations of others powerfully shape human behaviors. This dissertation investigates how culture may influence the conformity to and perception of social norms. Specifically, I focus on individualism vs. collectivism, a cultural variable that characterizes the extent to which people conceptualize themselves in the context of social relationships. This work demonstrates that the developmental trajectory of norm susceptibility during adolescence and early adulthood are distinct in collectivist vs. individualist cultures, and that in early stages of the coronavirus pandemic (COVID-19), collectivists show higher levels of normative perception that other people practice preventive health behaviors.Chapter 1 introduces past research on cultural and developmental influences on norm conformity, summarizes the rationale for focusing on individualism-collectivism as a key cultural dimension, and presents an overview of the research and methods in this dissertation. Chapter 2 investigates the developmental trajectory of social norm susceptibility in a collectivist culture (China), providing preliminary evidence that the developmental trajectory of social norm susceptibility in Chinese adolescents may be different from trajectories previously observed in U.S. and European samples. Chapter 3 concurrently recruited adolescents and young adults from the U.S. and China, and provided a direct cultural comparison in the developmental trajectory of social norm conformity. Results from this chapter demonstrate that cultural background moderates age-differences in social norm conformity: whereas U.S. participants showed a steady decrease in conformity in late adolescence, we did not observe the same trend in Chinese participants. These findings suggest that the developmental trajectory of social norm conformity may depend on cultural context. In Chapter 4, we demonstrated that collectivism is associated with higher levels of normative perception related to COVID-19 preventive behaviors. Further, at a country level, more collectivist countries showed lower growth rates in both COVID-19 confirmed cases and deaths. Chapter 5 synthesizes findings across chapters and highlights new avenues for future research. Overall, these findings indicate how cultural context affects the developmental trajectory and perception of social norms, providing initial evidence that cultural differences may be relevant to public health campaigns aimed at adolescents and young adults, or during crises like COVID-19.