It has been proposed that contextual fear conditioning depends on 2 processes: (a) construction of a conjunctive representation of the features that make up the context and (b) association of the representation with shock. Support for this view comes from studies indicating that prior exposure to the conditioning context facilitates contextual fear conditioning supported by immediate shock. Thus, conditioning produced by immediate shock is to the memory representation of the preexposed context, which is activated by retrieval cues associated with this context. The authors' experiments support this interpretation and indicate that this process depends on an intact hippocampal formation. These results support the hypothesis that the hippocampal formation supports contextual fear conditioning by storing a conjunctive representation of context.