Recent developments in the structural analysis of GaN and AIN surfaces are reviewed, and the implications of these structures for molecular beam epitaxial growth are discussed. The GaN(0001), AIN(10 (1) over bar0), and GaN(160) surfaces are all found to be terminated by metallic layers containing approximately one bilayer of Ga or Al atoms. However, in contrast to GaN(0001) where the Ga bilayer exists in an incommensurate, fluid-like state at room temperature, the metallic layers for AIN(0001) and GaN(10 (1) over bar0) form large-unit-cell commensurate structures with static atomic arrangements. Small amounts of H on the GaN(0001) surface leads to facet formation on the surface, whereas larger amounts of H produce a 2X2 surface arrangement that displaces the Ga bilayer. A possible model for the H-terminated GaN(1 0 (1) over bar1) surface is introduced and first-principles total energy calculations employing a finite temperature thermodynamics approach are employed to determine the conditions in which it could be stable. 0 2005 American Vacuum Society.