Pax proteins (called Paired box protein) regulate processes related to the division and differentiation of many cell types during embryonic and postnatal development in different animal species. Pax genes are evolutionarily conserved, their homologs found in the genome of nematodes and insects, and amphibians, fish, birds and mammals. No genes or functional abnormalities of the Pax proteins can lead to malignant transformation. In this paper, the structure and functions of Pax factors and their interaction with other proteins.