Book excerpt: While the effects of spontaneous ordering or composition modulation on the properties of semiconductors and optoelectronic devices have been studied with great interest over the past several years, an understanding of the physics and chemistry of these two related phenomena is still in its infancy. This book brings together researchers from around the world to address issues concerning the physics, chemistry and growth parameters for spontaneous ordering and composition modulation. Developments in the use of artificial patterning to obtain new structured materials on a microscopic scale are featured. Advances in characterization techniques are also presented. Topics include: spontaneous ordering; self-assembled structures and quantum dots; self-organized epitaxial structures; composition modulation studies and optoelectronic materials.