What do people conceal from others, and why? Despite the importance of concealing information as a way to establish boundaries between the self and others, avoid stigma, and define the situation, sociology is missing a comprehensive understanding of what people conceal, as well as a general account of concealment that is broadly applicable to most types of concealable matters. In this paper, we address these gaps in knowledge in two ways. First, we examine a wide range of concealable topics, and investigate individual- and group-level differences in what people conceal. Second, we propose that norms of concealment and a desire for autonomy motivate concealment across a range of situations and matters. We find that norms and autonomy predict concealment. Our findings constitute a general explanation of what motivates individuals to conceal, and a way to augment and synthesize previously disconnected literatures.