Stellar-mass black holes (3 M⊙≲MBH≲150 M⊙) are the natural product of the evolution of heavy stars (Mstar≳20 M⊙). In our Galaxy, we expect that 108–109 stellar-mass black holes have been formed from the gravitational collapse of heavy stars, but currently we know fewer than 100 objects. We also know of ∼100 stellar-mass black holes in other galaxies, most of them discovered by gravitational wave observatories in the past 10 years. The detection of black holes is indeed extremely challenging and possible only in very special cases. This article is a short review on the physics and astrophysics of stellar-mass black holes, including Galactic and extragalactic black holes in X-ray binaries, black holes in astrometric binaries, isolated black holes, and black holes in compact binaries. The article also addresses some important open issues and introduces the idea of a possible interstellar mission to the closest black hole.