This book contains nineteen of the twenty papers which were pre sented at the conference on "Heterogeneous Kinetics at Elevated Tem peratures" held on September 8, 9 and 10, 1969 at the University of Pennsylvania. The papers are concerned primarily with the kinetics of inter facial reactions between the gaseous phase and a condensed phase and include pertinent topics in microscopic and macroscopic trans~ port phenomena. Several of the more recent advances in experimen tal techniques are covered, since progress in the interpretation of kinetic phenomena seems to be intimately connected with advances in experimental method. The discussion after each paper, as well as the general discussion at the end of the meeting, have been included in a strictly edited version; the philosophy being to include only those topics and questions which were not dealt with in the final versions of the manuscripts. The Chairmen (editors) would like to express their thanks to Professor C. B. Alcock for vigorously leading the final discussion period and for his entertaining after-dinner remarks on the evening of the conference banquet. The Chairmen would also like to place on record their indeptedness to Dr. D. R. Gaskell who, with the assistance of Mr. P. C. Shumaker, was largely responsible for the efficient technical arrangements of the meeting; to Dr. P. Entner and the willing group of graduate students for recording the dis cussions and for other organizational assistance; to Miss L.