vi The amalgamation of individual approaches and results from various schools into a comprehensive scientific theory, which can be generally appreciated throughout the international scientific com­ munity, is oftendifficult and time consuming. We believe that one of the best ways to give a complete and clear presentation of a theoryis to include a review of the developmental history of that theory. We are convinced that explaining a theory in a historical perspectiveis essential for a proper understanding ofits present state and for a sound choice of future developments. So we have endeavored to present a complete picture of investi­ gations performed in both Western and Soviet nations. We understand that Soviet investigations are less familiar to English-speaking readers due to the languagebarrier and the obvious sad circumstances of the interruption of scientific connections before and after World War II, because of this there is an emphasis on Soviet publications in the bibliography. Our attempt to present a comprehensive picture has made our book rather large becauseit has had to include some fundamentals of thermochemistry and kinetics as well as self-ignition and flame propagation invarious conditions. We have also included stability problems in some detail but we have had to leave out the problems of combustion of solid propellants and detonation. We hope that our bookwill be useful to the reader wishing to learn about both the present state of combustion theory and howit originated due to the efforts of many people from different countries. Ya.B.Z.