Polymeric cocrystalline forms, that is, structures were a polymeric host and a low-molecular-mass guest are cocrystallized, were early recognized, and in many cases also well characterized by X-ray diffraction studies. However, only in the last two decades cocrystalline forms have received attention in material science, due to the ability (of few of them) to maintain an ordered polymer host structure even after guest removal, thus leading to the formation of nanoporous-crystalline forms, for which many applications in the fields of molecular separation and sensors have been proposed. Moreover, in the last decade, an accurate control of the orientation of the polymer cocrystalline phases has been achieved, thus leading to a control of the orientation of the guest molecules, not only in the crystalline phase but also in macroscopic films. In addition, on the basis of this orientation control, in the last few years, cocrystalline films where active molecules are present as guests of polymer cocrystalline phases have been proposed for optical, magnetic and electric applications. In the last few years, it has been also discovered that polymer cocrystallization, when induced by nonracemic guest molecules, can produce stable chiral optical films. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012