We are monitoring the young star GQ Lup and its
sub-stellar companion since a few years with several
imaging and spectroscopic observations per year.
In this paper, we will present preliminary results
on the orbital motion, orbital inclination,
and photometric variability of the companion.
The mass estimate for the companion from both
fitting observed spectra to atmospheric models
and formation models implies that it is either
a massive planet or a low-mass brown dwarf.