Black holes and singularities in string theory

This is a summary of a lecture I gave at the workshop on dynamics and thermodynamics of black holes and naked singularities at Politecnico Milano. It is directed to a non-expert audience and reviews several ways in which string theory accounts for black hole microstates. In particular, I give an elementary introduction to the correspondence principle by Horowitz/Polchinski, to the state counting for the three-charge black hole by Strominger and Vafa, and to the recent proposal by Mathur et al. concerning the gravity description of black hole microstates. The second part of the lecture is dedicated to naked singularities and reviews an argument by Horowitz and Myers why naked singularities are not necessarily bad. Finally, I comment on a possible resolution of singularities in Born-Infeld type gravity theories.