The performance of a wide range of modern magnetic thin-film materials for information storage is found to depend dramatically on grain nucleation and coherence at interfaces. Three such systems, Fe/Pt Multilayers, CO/Pt Multilayers, and CoCrTa/Cr bilayers are considered here. High-resolution electron Microscopy (HREM) shows that ordered CoPt and FePt L1o structures can be formed and oriented, using coherence with the substrate, with their magnetically easy c-axes perpendicular to the film plane. This orientation results in the perpendicular magnetization required for Magneto-optic recording Media. Different sputtering gases used in producing CO/Pt Multilayers result in varying degrees of interfacial intermixing, which is shown to strongly affect the perpendicular magnetic anisotropy energy. The required high in-plane coercivity of longitudinal recording media is also correlated with the observed interface coherence and the resulting oriented growth of CoCrTa with the magnetically hard <110> axis perpendicular to the film plane. Many features of the microstructure can be observed directly at the atomic level by HREM, and so the usefulness of this technique is emphasized in this paper.