This chapter considers the second important application of quantum gravity - quantum cosmology. The central concept of minisuperspace is introduced and applied to the quantization of a Friedmann universe. Inhomogeneities are taken into account in a perturbative sense. A central role of this chapter is played by the discussion of boundary conditions, notably the no-boundary proposal by Hartle and Hawking and the tunneling condition by Vilenkin, and their comparison. The chapter concludes with a section on loop quantum cosmology.