Adulthood holds a paradoxical position in sociology. It is a central category insofar as it provides the unarticulated background to a majority of social enquiries, but it is largely defined by default as the taken-for-granted status of the social actor and the middle stage of life. Yet, the meaning of adulthood is rarely addressed directly. Those researchers who do, tend to note its transformation from a social to a psychological category. This article elaborates the social constitution of adulthood and thus offers an alternative as well as complementary view. First, the article explicates the status of adulthood in sociology and in everyday discourse, and identifies a standard model of adulthood against which individuals' practices are prevalently judged. Second, it outlines the prolonged adolescence thesis, an entrenched position in sociology and everyday discourse that posits an increasing number of individuals as deferring or rejecting adulthood. Finally, the article proposes a reconceptualization along recognition-theoretical lines and suggests that the association of adulthood with full personhood is the meaningful constant of this ultimately social category.