  This article summarizes the latest results on the proton-to-electron mass
ratio $\mu$ derived from H$_2$ observations at high redshift in the light of
possible variations of fundamental physical constants.
  The focus lies on UVES observations of the past years as enormous progress
was achieved since the first positive results on $\Delta\mu/\mu$ were
published. With the better understanding of systematics, dedicated observation
runs, and numerous approaches to improve wavelength calibration accuracy, all
current findings are in reasonable good agreement with no variation and provide
an upper limit of $\Delta\mu/\mu$ $< 1\times 10^{-5}$ for the redshift range of
$2 <$ z $< 3$.
