  This is an introductory, up-to-date review of the essentials of black hole
thermodynamics. The main topics surveyed are: (i) the four laws of
thermodynamics as applied to a black hole horizon, and the current status of
their proofs; (ii) different definitions of horizons, and their unique
properties; (iii) the nature of black hole entropy, its quantum and stringy
corrections, and ultimate origin from quantum gravity microstates; (iv) the
focusing law for the area/entropy; and finally (v) the holographic principle,
and how we can use it to learn about the information inside black holes.
