Cell motility and morphogenesis are the end products of highly coordinated cellular activities involving cytoskeletal structures, the machinery for cell adhesion, and signaling networks. Among the hundreds of proteins that contribute to cellular movements and shape changes, only a few lie at the hub of these activities by virtue of interacting directly with cytoskeletal, cell adhesion, and signal transduction proteins. One such protein is IQGAP1, the first known member of a protein family that has a widespread, but curiously sporadic phylogenetic distribution. IQGAP1 can bind directly to an impressive collection of other proteins, including F-actin; the microtubule interacting protein, CLIP-170; the cell adhesion factor, E-cadherin;-catenin, which couples E-cadherin to cortical actin networks and also regulates gene expression through the wnt signalling pathway; calmodulin; and activated forms of the small G proteins, Rac1 and Cdc42, which are intimately involved in regulating cortical actin networks. IQGAP1 is widely expressed among mammalian cell types, is most concentrated in cortical regions rich in actin filaments, and has been implicated in the control of cellular motility and morphogenesis through regulation of actin organization, cell-cell adhesion, microtubule stability, and small G proteins. Mammals express at least two different IQGAPs, which are 50% identical in amino acid sequence. The functions of IQGAP1 at the cellular and organismal levels are in the process of being unraveled, and very little is known about other mammalian IQGAPs. In contrast, genetic approaches using Dictyostelium and yeast have revealed specific and essential roles in cytokinesis for IQGAPs expressed in those organisms. We present this overview of IQGAPs now in light of growing interest in these proteins among cell biologists, and the fact that, until now, no comprehensive reviews dedicated to this protein family have been published in peer-reviewed journals.