  The most compelling evidences for the existence of stellar-mass black holes
have been obtained through observations of X-ray binary systems. The
application of classical methods and the development of new techniques have
allowed us to increase the number of stellar-mass black holes known. I
summarize here the observational signatures of the black holes, such as the
mass determination, the event horizon and the spin. I also present some
observational results on the Galactic centre black hole.
