Pax-6 is a member of the Pax gene class and encodes a protein containing a paired domain and a homeodomain. The molecular characterization of Pax-6 genes from species of different animal phyla and the analysis of Pax-6 function in the developing eyes and central nervous system of vertebrates, Drosophila melanogaster, and Caenorhabditis elegans suggest that Pax-6 homologues share conserved functions. In this review, we present recent data on the structural and functional characterization of Pax-6 homologues from species of different animal phyla. We discuss the implications of these findings for our understanding of the development and evolution of eyes and nervous systems.