Microfilaments are composed of two helicoidal chains of the protein actin. Microfilaments help the cell keep its shape and participate in some types of cell-to-cell junctions. They are instrumental in certain structures such as pseudopodia.

Additionally, actin microfilaments are also often found where choreographed movements occur within the cell. They are also important for cytokinesis and actin microfilaments play an integral role with the protein myosin in muscular contraction. Actin microfilaments are present in regular arrays associated with myosin filaments in muscle tissue. The interaction also of actin and myosin is also central to cytoplasmic streaming, which describes the flowing of cytoplasm for reorganization of cellular contents and in some cases, locomotion.