This chapter introduces compact objects, white dwarfs, neutron stars, and black holes. The properties of compact objects are summarized as the typical radius, mass, and compactness. These compact objects are the final end point in stellar evolution. The stellar evolution in terms of the mass of the star is outlined, focusing on the burning stages and the final collapse of the star, either as a white dwarf or in a core-collapse supernova. Historical notes are given for the discovery of white dwarfs and neutron stars.