  A small group of X-ray binaries currently provides the best evidence for the
existence of stellar-mass black holes. These objects are interacting binary
systems where the X-rays arise from accretion of material onto a compact object
(i.e. an object with a radius of less than a few hundred km). In some
favourable cases, optical studies of the companion star lead to dynamical mass
estimates for both components. In 17 cases, the mass of the compact object an
X-ray binary has been shown to exceed the maximum mass of a stable neutron star
(about 3 solar masses), which leads to the conclusion that these objects are
black holes. In this contribution I will review the basic properties of these
black hole binaries.
