Previous work shows that children view group membership and psychological traits in essentialist terms, perceiving them to be both biologically determined and stable across time. To what extent might individuals view mental states such as beliefs similarly? Given that beliefs are often based on experience and can change across time, one hypothesis is that beliefs on the whole do not elicit essentialism. An alternative hypothesis, however, is that some beliefs may be perceived as inherited and stable over time characteristics associated with essentialism. In three studies, we examined two aspects of psychological essentialism regarding three different types of beliefs (religious beliefs, factual beliefs, and opinions) in 8- to 10-year-old children and adults, asking whether beliefs are seen as (a) biologically based and/or (b) stable across time. Both children and adults distinguished among belief types when considering biology; opinions were perceived to be more rooted in biology than were other beliefs. By contrast, fewer consistent differences emerged when children and adults considered stability. For example, both children and adults perceived opinions and factual beliefs to be equally changeable. Finally, although children typically perceived beliefs to be more rooted in biology than adults, more specific patterns across belief types (e.g., perceiving opinions to be more rooted in biology than religious beliefs) remained relatively stable across age groups. Thus, development and social learning may play a larger role in perceptions of the biological component of essentialism than in judgments of particular beliefs. We discuss implications for literatures on essentialism, religious cognition, and social cognitive development. (C) 2016 Elsevier Inc. All rights reserved.