The actin cytoskeleton is a highly dynamic network composed of actin polymers and a large variety of associated proteins. The main functions of the actin cytoskeleton are to mediate cell motility and cell shape changes during the cell cycle and in response to extracellular stimuli, to organize the cytoplasm, and to generate mechanical forces within the cell. The reshaping and functions of the actin cytoskeleton are regulated by signaling pathways. Here we broadly review the actin cytoskeleton and the signaling pathways that regulate it. We place heavy emphasis on the yeast actin cytoskeleton.