In this chapter, a brief introduction is given to the quantum aspects of black holes. It is an important fact that black holes obey laws analogous to the laws of thermodynamics. Taking quantum theory into account, it becomes clear that black holes do in fact emit thermal radiation ("Hawking radiation") and possess an entropy. The physical meaning of Hawking temperature and black hole entropy is discussed in detail. These effects can only be observed if primordial black holes (relics from the early Universe) exist. The chapter therefore ends with a brief review of the current observational constraints on their existence.