Metal oxides constitute an extremely diverse class of materials, with virtually all types of electronic and magnetic behavior represented. These materials thus possess many properties that make them unique and potentially important for future technologies. No other class of materials exhibits such a wide range of behavior: band gaps spanning the visible and UV; electronic properties ranging from superconducting to metallic to semiconducting to insulating; magnetic properties ranging from ferromagnetic to antiferroma gnetic; and dielectric properties ranging from low-k to ferroelectric and piezoelectric. In addition, metal oxides exhibit a wide range of crystal structures, including spinel, perovskite, and corundum. As a result, a variety of heteroepitaxial structures can be designed and synthesized. In this talk, I present recent results on three heteroepitaxial oxide systems that illustrate the fascinating interface physics and potential technological advantages of these materials: (1) SrTiO@sub 3@(001)/Si(001), (2) CoFe@sub 2@O@sub 4@(001)/MgO(001) and, (3) MgO(001)/Ag(001) and Pt(111)/@alpha@-Cr@sub 2@O@sub 3@(0001)/Pt(111)/@alpha@-Al@sub 2@O@sub 3@(0001). System 1 is of considerable interest as a high-k gate oxide in next-generation MOSFETs.@footnote 1@ System 2 is a model that permits us to investigate thin films of what appears to be a very promising high-magnetic-anisotropy, insulating ferrimagnet.@footnote 2@ System 3 allows us to examine the effects of polarizable metals on the optical, electronic and magnetic properties of ultrathin oxides that are within electronic screening lengths of the metal.@footnote 3@ Structural, electronic and magnetic properties of these systems, all grown by molecular beam epitaxy, will be presented. @FootnoteText@ @footnote 1@ R.A. KcKee et al., Phys. Rev. Lett. 72, 2741 (1994). @footnote 2@ Y. Suzuki et al., Appl. Phys. Lett. 68, 714 (1996). @footnote 3@ S. Altieri et al., Phys. Rev. B59, R2517 (1999).