c-Jun/AP-1 activation has been implicated in various, often opposing cellular responses. For example, although there is considerable evidence that c-Jun activation can be a positive step in the events leading a cell towards apoptosis, there are also many reports stating the opposite: that under certain circumstances c-Jun can inhibit apoptosis and promote proliferation or differentiation instead–and that these responses are important for normal mammalian development. It is clear that the effects of c-Jun on cellular responses depend strongly on the cell type and the context of other regulatory influences that the cell is receiving. This review focuses on recent developments in understanding how activation of JNK and c-Jun contributes to different cellular responses.