We briefly introduce black holes in the theory of general relativity and study their thermodynamic properties. We then move to supersymmetric black holes, which are solutions to superstring theories. As an example we concentrate on the D1-D5 brane system in five dimensions, in the context of compactifications of type IIB superstring theory on a 5-torus. We compute the macroscopic (Bekenstein-Hawking) entropy of the corresponding black hole. We then give a microscopic interpretation of this result in terms of string microstates, following the work of Strominger and Vafa. We end by mentioning some current open problems in black hole physics. |