About the book: year / Black holes are the most mysterious cosmic objects predicted by the general theory of relativity. In this review article we will focus on some interesting properties of classical black holes. If we supplement the general theory of relativity with quantum mechanical concepts, black holes cease to be absolutely black. In fact, they emit thermal radiation. The existence of this thermal radiation leads to a number of paradoxes. If we additionally use string theory as a quantum theory of gravity, some of the paradoxes are resolved. This leads to some interesting changes in our conceptual understanding of spacetime.