Protein kinase C (PKC) is a family of serine/threonine kinases implicated in intracellular signalling events triggered in response to a large variety of agonists. Currently, 11 mammalian PKC isoforms have been identified which are divided into three groups, the calcium-dependent, the non-calcium-dependent and the atypical isoforms. Common to all members is the presence of an aminoterminal regulatory domain, which renders the kinase inactive by interacting with the carboxyterminal catalytic domain. Thus, intracellular PKC activation requires the release of this autoinhibitory restraint, which, as this review summarizes, may involve both interactions with lipids and proteins. Furthermore, post-translational PKC phosphorylation events, required to convert PKC to an activation competent state, are discussed.