The aim of this review is to underline the redundancy of down-regulation pathways for p53, at the light of the two more important degradative systems: calpains and ubiquitin-dependent pathways. The MDM2 feed-back loop is also illustrated, as well as the phosphorylative/dephosphorylative regulation of the latent and active p53 isoforms. The mechanisms prolonging p53 half life, following irradiation, are also discussed.