Nanoelectronics is a broad topic that spans molecular devices to silicon field-effect transistors. While the development of nanoscale silicon devices is an important topic, the focus here will be on the challengers to silicon such as molecules, carbon nanotubes, and nanowires. In high performance applications like computation or communications, the challengers might be able to provide devices that are about as fast, and about as small as those that will be made in the near future in silicon. It is not in terms of performance that silicon will be challenged. The real potential of the challengers is that they may eventually provide about the same performance as silicon for a lower price.