String theory is a promising candidate for a quantum theory of gravity and a unified theory of all forces and particles. I will briefly summarize the current status of this theory and discuss some recent results. The most important results involve describing quantum states of black holes in terms of strings, which has provided a fundamental explanation of black hole entropy and Hawking radiation. Further investigation of this connection between black holes and strings has led to a completely new nonperturbative formulation of string theory. ©2001 American Institute of Physics.