Actin is an extremely abundant protein that comprises a dynamic polymeric network present in all eukaryotic cells and known as the actin cytoskeleton. The structure and function of the actin cytoskeleton is modulated by a plethora of actin-binding proteins and performs a diverse range of cellular roles. Well-documented functions for actin include: providing the molecular tracks for cytoplasmic streaming and organelle movements; formation of tethers that guide the cell plate to the division site during cytokinesis; and coordinating the elaborate cytoplasmic responses to extra- and intracellular signals. This work covers topics related to the plant actin cytoskeleton. Because the actin cytoskeleton impinges on a multitude of processes critical for plant growth and development, as well as for responses to the environment, the text should be invaluable to any researcher, from the advanced undergraduate to the senior investigator, who is interested in these areas of plant cell biology.