Scandium nitride is an interesting transitional metal nitride semiconductor with a simple crystal structure (rocksalt). Part of the interest in ScN is as a lower bandgap material (Eg = 2.1 eV) which can be combined with GaN to form novel heterostructures or alloys. In particular, GaN has a lattice constant close to ScN (both about 4.5Å ); it may therefore be possible to form an alloy with band gap in the range 2.1-3.4 eV. However, since ScN is rocksalt while GaN is zincblende or wurtzite, it is not clear that a simple alloy or interface can be formed. We have first investigated the growth of pure ScN on magnesium oxide (001) substrates by molecular beam epitaxy (MBE) using a RF-plasma source and a scandium effusion cell. The Sc/N flux ratio was found to be critical in determining the structural, optical, and electronic properties of the grown epitaxial layers. Under N-rich conditions, the growth is epitaxial, and we find atomically smooth terraces separated by steps having height a/2. Films grown N-rich are stoichiometric and transparent with a direct optical transition at 2.15 eV; further efforts are underway to experimentally verify the theoretically predicted indirect transition near 1 eV. We have begun to investigate the growth of GaN/ScN(001). First, we grew ScN(001) at growth temperature 850°C; next, we initiated GaN growth at reduced substrate temperature 550°C under Ga-rich conditions. After several minutes, the growth temperature was increased to 750°C, and the Ga flux was reduced but still maintaining Ga rich conditions. Reflection High Energy Electron Diffraction (RHEED) showed a pattern consistent with cubic GaN(001). X-ray diffraction showed only one peak beside the MgO substrate peak revealing that the GaN film is cubic having the same (002) orientation as the ScN(001) layer. A Sc-Ga-N layer was also grown on MgO(001) with growth temperature at 850°C. Structural and optical properties will be presented.