Structural observations provide persuasive evidence for the existence of a cortical network of endoplasmic reticulum (ER) in a large number of plant and animal cells. The network in plants generally possesses a polygonal pattern in which smooth, tubular elements are joined by intervening lamellar segments. The individual elements of ER are often positioned extremely close to the plasma membrane (PM), and may form appositional contacts, but fusion does not occur. The network arises at cytokinesis and establishes continuity between the cortical ER of daughter cells in the form of tightly furled membrane tubules that traverse the plasmodesmata. The specific function of the cortical ER complex is unknown but different possibilities seem attractive. It may serve key roles in anchoring the cytoskeleton and in facilitating secretion. The cortical ER might also participate in the communication of signals between the exterior of the cell and cytoplasm. As a consequence of its ability to release and/or sequester Ca, the ER could control the cytoplasmic activity of this ion and thus a host of physiologically and developmentally important reactions.