  Accurate measurements of interstellar deuterium abundances along lines of
sight extending out to several hundred parsecs by FUSE and other instruments is
making D/H a useful tool for understanding Galactic chemical evolution. We find
that the gas inside of the Local Bubble is chemically homogeneous, but that
large variations in D/H beyond the Local Bubble are real and challenge present
concepts of chemical evolution. A new set of models is needed that will include
spatially dependent infall of relatively unprocessed material, depletion of D
onto grains, and appropriate mixing timescales. $
