In this the 50th anniversary year of the AVS and the AVS Symposium, this article is offered as one in a series of topical review articles to celebrate the role of this community to the progress in nanofabrication technology. The emphasis of the article is on the principles and limits of the various pattern formation techniques which have emerged as important tools in the research of nanoscale devices and structures. Topics such as e-beam lithography, proximal probes, imprint lithography, self assembly, and directed assembly are all discussed.