The observational evidence for the existence of black holes has grown significantly over recent decades. Stellar-mass black holes are detected as X-ray sources in binary systems, while supermassive black holes, with masses more than a million times the mass of the Sun, lurk in the nuclei of galaxies. These proceedings provide a useful and up-to-date overview of the observations of black holes in binaries, in the center of the Milky Way, and in the nuclei of galaxies, presented by leading expert astronomers. Special attention is given to the formation (including the recent evidence from gamma-ray bursts), physical properties, and demographics of black holes.