  I summarize recent near-infrared spectroscopy of the microquasar GRS 1915+105
with the ESO/VLT which allowed to (i) identify the donor and (ii) measure the
orbital period and radial velocity amplitude. Assuming that the jet ejections
occur perpendicular to the accretion disk and orbital plane, the mass of the
black hole is determined to M = 14 +- 4 solar masses. I discuss the
implications of this mass determination on (a) the understanding of the
large-amplitude X-ray variability in GRS 1915+105, (b) binary formation
scenarios, and (c) models to explain the stable QPO frequencies in GRS 1915+105
and GRO J1655-40.
