Block copolymers (BCPs) have received great attention for the past 40 years but only within the past decade have they been seriously considered for nanotechnological applications. Their applicability to nanotechnology stems from the scale of the microdomains and the convenient tunability of size, shape, and periodicity afforded by changing their molecular parameters. The use of the tensorial physical properties of BCPs in such areas as transport, mechanical, electrical, and optical properties will provide substantial benefits in the future. In this review article, we first focus on the current efforts to utilize BCPs in nanotechnologies including nanostructured membranes, BCP templates for narroparticle synthesis, photonic crystals, and high-density information storage media. In order to realize these applications, control over microdomain spatial and orientational order is paramount. This article reviews various methods to control BCP microdomain structures in the bulk state as well as in thin films. A variety of biases such as mechanical flow fields, electric fields, temperature gradients, and surface interactions can manipulate the microstructures of BCPs. A particular emphasis is made on two approaches, epitaxy and graphoepitaxy, and their combinations. Manipulation of BCP microdomain structures employing multiple external fields promises realization of many potential nanotechnological applications. (C) 2003 Elsevier Ltd. All rights reserved.