The shapes of plant cells, which are defined by their surrounding walls, are often important for cell function. The cytoskeleton plays key roles in determining plant cell shape, mainly by influencing the patterns in which wall materials are deposited in expanding cells. Studies employing cytoskeleton-disrupting drugs, together with studies of mutants with cytoskeletal defects, have demonstrated that both microtubules and actin filaments are critical for all modes of cell expansion, although their precise roles remain poorly understood. In recent years, however, significant progress has been made in understanding the contributions of a variety of proteins that influence cell shape by regulating the organization and polymerization of cytoskeletal filaments in expanding cells.