The existence of stellar-mass black holes is now well established but the recent LIGO/Virgo results suggest that the black hole mass distribution of stellar-mass black holes is more complex than that derived so far from measurements using X-ray binaries. I will explain how dynamical mass measurements have been obtained for the black holes in these single-lined spectroscopic binaries and discuss several biases that may help explain the differences between masses from LIGO/Virgo events and X-ray binaries. The goals are to investigate how black holes forms and, in particular, to investigate if intermediate-mass black holes exist. Intermediate-mass black holes may well be necessary to explain the presence of super-massive black holes when the universe was less than 1 Gyr old. I will finish by showing results from our recent attempts to find
intermediate-mass black holes using geometrical constraints.