We have recently measured the refractive index of Hydrogen Fluoride gas from 2.5 to 2.9 microns, with a wavelength resolution of .004 microns 1. We will describe the theoretical modeling of those results and discuss their implications in this paper. The data of reference 1 are shown in figure 1. It is clear that resonant dispersion dominates the refractive index over much of the measurement region. The solid line is the best theoretical fit to our data. On the basis of our theoretical modeling, we feel that these results are significant because resonant dispersion effects may be an important factor in laser medium quality for certain lines. In order to determine the extent of these effects, further research is required, particularly for Deuterium Fluoride.