This book contains 18 invited contributions to the first Inter­ national Symposium on Order-Disorder Transformations in Alloys+. They cover the major aspects of this group of phase transformations. Although structural order-disorder transformations have been investigated for over 50 years the invited papers, the research papers - whose titles and authors are listed in the appendix - and the discussions at the Symposium have demonstrated very active continued interest and con­ siderable recent progress in the subject. This is true for theoretical work as weIl as for experimental studies and for the development of materials whose properties result from order-disorder transformations. + Some major national conferences on ordering were held in the USA and in the USSR in recent years; the proceedings are available in the following pUblications: Local Atomic Arrangements Studied by X-Ray Diffraction, Gordon & Breach, New York 1966 2 Ordered Alloys, Claitor's Publ. Div. , Baton Rouge, La. 1970 3 Summaries of the Proceedings of the 2nd Union Conference on Atomic Ordering and its Influence on the Properties of Alloys, Naukova Dumka, Kiev 1966 4 Atomic Ordering and its Influence on the Properties of Alloys, Naukova Dumka, Kiev 1968 5 Atomic Ordering and its Influence on the Properties of Alloys, TGU, Tomsk 1973 111 In assembling these papers it vas attempted to compile a systematic and approximately complete compendium of the sUbject.