Reorganization of the actin cytoskeleton is essential for cellular processes during animal development. Cofilin and actin depolymerizing factor (ADF) are potent actin‐binding proteins that sever and depolymerize actin filaments, acting to generate the dynamics of the actin cytoskeleton. The activity of cofilin is spatially and temporally regulated by a variety of intracellular molecular mechanisms. Cofilin is regulated by cofilin binding molecules, is phosphorylated at Ser‐3 (inactivation) by LIM‐kinases (LIMKs) and testicular protein kinases (TESKs), and is dephosphorylated (reactivation) by slingshot protein phosphatases (SSHs). Although studies of the molecular mechanisms of cofilin‐induced reorganization of the actin cytoskeleton have been ongoing for decades, the multicellular functions of cofilin and its regulation in development are just becoming apparent. This review describes the molecular mechanisms of generating actin dynamics by cofilin and the intracellular signaling pathways for regulating cofilin activity. Furthermore, recent findings of the roles of cofilin in the development of several tissues and organs, especially neural tissues and cells, in model animals are described. Recent developmental studies have indicated that cofilin and its regulatory mechanisms are involved in cellular proliferation and migration, the establishment of cellular polarity, and the dynamic regulation of organ morphology.