Elemental abundances in Milky Way halo gas

The gas-phase and dust-phase abundances of chemical elements in Milky Way halo gas provide important information about the processes that transfer gas and dust between the Galactic disk and halo. This article is a brief review of recent Hubble Space Telescope determinations of the abundances of important elemental constituents of the interstellar gas and dust in the inner and outer Milky Way halo and high velocity clouds. These quantities serve as useful reference values for comparisons with the abundances determined for extragalactic systems.