  We present column density measurements of the HD molecule in the interstellar
gas toward 17 Galactic stars. The values for the seven most heavily reddened
sightlines, with E(B-V) = 0.38-0.72, are derived from observations with the Far
Ultraviolet Spectroscopic Explorer (FUSE). The other ten values are from a
reanalysis of spectra obtained with Copernicus. In all cases, high-resolution
ground-based observations of KI and/or the CH molecule were used to constrain
the gas velocity structure and to correct for saturation effects. Comparisons
of the column densities HD, CH, CN, and KI in these 17 sightlines indicate that
HD is most tightly correlated with CH. Stringent lower limits to the
interstellar D/H ratio, derived from the HD/2H2 ratio, range from 3.7 10^(-7)
to 4.3 10^(-6). Our results also suggest that the HD/H2 ratio increases with
the molecular fraction f(H2) and that the interstellar D/H ratio might be
obtained from HD by probing clouds with f(H2) = 1. Finally, we note an apparent
relationship between the molecular fractions of hydrogen and deuterium.
