Gab proteins, including mammalian Gab1, Gab2, Gab3, Drosophila DOS and Caenorhabditis elegans Soc1, comprise a growing family of scaffolding/docking molecules involved in multiple signaling pathways mediated by receptor tyrosine kinases (RTKs) and non-RTK receptors. This paper reviews the structure/function relationships of Gab proteins and their biological roles during normal growth, differentiation and development programs.