This year's meeting of Nobel laureates unites the founding fathers of heterostructure devices, Alferov, Esaki, and Kroemer. Their lectures will demonstrate the immense importance of these structures for new kinds of optical and electronic devices. My contribution will deal with some fundamental phenomena in physics which can be observed particularly well in heterostructures. Mention will, of course, be made also of the most recent research in the field of the quantum Hall effect and the single-electron transistor.