The actin cytoskeleton provides force for dynamic cellular processes, such as motility, morphogenesis, cell division, endocytosis, and phagocytosis. The organization and dynamics of actin filament must be precisely controlled during these processes, and consequently defects in regulation of the actin cytoskeleton lead to various diseases including cancer progression, as well as neurological and immunological disorders. Our group uses a wide range of biophysical, biochemical, cell biological, and genetic approaches to uncover the general principles underlying regulation of the actin cytoskeleton, and to reveal how defects in actin dynamics affect the physiological functions of cells.