The recent discovery of several p53 homologs has uncovered a p53 superfamily of transcription factors that can trigger cell cycle arrest and apoptosis. The challenge now is to understand the similarities and differences between family members especially in terms of their regulation and potential for physical or genetic interactions with one another. This review summarizes recent progress in understanding the structure-function relationship within the p53 family. The new family members, p63 and p73, have an additional conserved domain at their C-termini which may have a regulatory function. The structure of this domain (a SAM domain) suggests that it is a protein-protein interaction module that may be involved in developmental processes. The oligomerization domains of p53 family members, while conserved in sequence and three-dimensional structure do not interact appreciably with other family members, but do mediate interactions between the multiple splice variants from an individual gene.