Modulated Structure Materials arise in two basic ways. One is through the natural tendency that certain materials have to develoo stable modulations. Tynical examples of this catenory are the lonn oeriod superlattices, the spinodal alloys and other ordered structures. Another way to introduce nodulation into a basic is throuqh our own intervention, that is ~v artificial structure techninues. Such examples as the conposition nodulated films and the seniconductor superlattices have recently received apnreciable attention not only for their noble and unusual nrooerties but also for their practical applications in hiqh technolony areas. The NATO Advanced Study Institute on Modulated Structure ~'laterials which was held June 15-25, 1983 in t1alene-Chania, Greece, aimed at brinninq tonether international authorities and active researchers to discuss in-depth current knowledne and new develop­ ments in both natural and artificial modulated structure materials. Up to this time, the Editor has received indications that the Institute served well its purpose. The fifteen carefully selected invited speakers qave outstandinq lectures on all aspects of modulated structures. The lectures were followed by extensive and lively discussions amonq all participants. It should be noted that on two occasions discussion panels were formed to address some of the fundamental aspects of modulated structures in view of the imnressive result~ of advanced experimental techniaues (lattice ann structure imaqinq techniaues in hinh resolution electron microscoP", X-ray and neutron diffraction Methods, etc.