Cellular morphology, adhesion, and motility occur through the reorganization of the actin cytoskeleton. This reorganization of actin filaments occurs through the interactions between actin and actin binding proteins. Actin-binding proteins regulate the polymerization and depolymerization of actin, connect actin-based structures to membranes and to other cytoskeletal elements, power the movement of actin filaments, and cross-link actin filaments into bundles. Actin related proteins (Arp) 2/3 complex is an actin polymerization inducing complex that includes Arp2, Arp3, p41-Arc, p34-Arc, p21-Arc, p20 Arc, and p16-Arc. The Arp2 and Arp3 subunits may nucleate actin polymerization, while the p41-Arc subunit is a WD repeat-containing protein that may regulate both the activity and localization of the Arp2/3 complex. Arp3, p34-Arc, and p21-Arc are localized to the lamellipodia of stationary and locomoting fibroblasts. Both WASP and Abp1p are acidic sequence-containing proteins that activate the Arp2/3 complex. However, WASP binds actin monomers, while the endocytosis-related Abp1p protein binds actin filaments. Thus, Arp2/3 complex may regulate actin polymerization in specific cell locations through interaction with actin binding Arp2/3 activators.