  I review the astrophysical insights arising from high-precision astrometric
observations of X-ray binary systems, focussing primarily (but not exclusively)
on recent results with very long baseline interferometry. Accurate,
model-independent distances from geometric parallax measurements can help
determine physical parameters of the host binary system and constrain black
hole spins via broadband X-ray spectral modelling. Long-term proper motion
studies, combined with binary evolution calculations, can provide observational
constraints on the formation mechanism of black holes. Finally, the astrometric
residuals from parallax and proper motion fits can provide information on
orbital sizes and jet physics. I end by discussing prospects for future
progress in this field.
