Flowering plants rely on the highly polarized process of pollen tube growth for delivery of the sperm cells and thus for sexual reproduction. Although it has long been known that the actin cytoskeleton is necessary for pollen grain germination and tube growth, the precise structure of the actin arrays and their regulation by actin-associated proteins is only starting to be uncovered. Long, axially-oriented bundles of actin are abundant in the shank of pollen tubes but absent in their apices. These bundles function as tracks for the myosindependent cytoplasmic streaming that transports organelles and secretory vesicles in a bi-directional, reverse-fountain pattern. Exocytosis of the vesicles, which is required for cell growth, is restricted to the apex of the pollen tube. To understand these growth-dependent motile processes, actin as well as many actin-binding proteins, are being isolated from pollen and characterized both in vitro and in vivo. Spatial modulation of the actin cytoskeleton may be governed in part by calcium, protons and small GTPases, which are asymmetrically distributed. Understanding how the actin cytoskeleton interacts with these different factors helps us explain the molecular basis of polarized pollen tube growth.