A common view supposes that dendritic cells (DCs) exist in two basic functional states: immature DCs induce tolerance to self, whereas mature DCs induce immunity to foreign antigens. However, the term 'mature' is often used not only functionally to designate immunogenic DCs but also as a phenotypic description of DCs expressing high levels of MHC, adhesion and co-stimulatory molecules. The recent realization that DCs can express such markers under non-immunogenic conditions raises the question of whether the two connotations of the term 'mature' should continue to be used interchangeably. Here, I discuss the origins of the maturation model and how terminology is evolving to better accommodate our current understanding of the function of DCs.