A monograph in German, el,Litled Allergie und allergische Erkrankungen, edited by the late Edmund Rajka, Corresponding Member of the Hungarian Academy of Sciences, was published in 1959. The second edition, revised and completed according to contemporary advances in allergology and immunology, was pub­ lished in Russian seven years later, in 1966. Both volumes dealt with the theore­ tical and clinical aspects of allergology and allergic diseases on the basis of the information emerging from fundamental immunological research. - Demand for an English version of the monograph was realized immediately after the second edition. Advances in the discipline of molecular biology, accu­ mulating immunological knowledge and changes in outlook had by then affected the entire view of clinical medicine. Allergology, recently also known as clinical immunology as it provides clues to practically all branches of clinical medicine, has ceased to be the chosen field of specialists. A knowledge in this field is now an essential prerequisite of modern clinical practice and research. It was in view of these facts that the compilation of this volume was begun; unfortunately, having already done the greater part of the work, Professor Rajka died suddenly. Regrettably, he did not live to see the publication of this book, to the editing of which he devoted so much time and energy. Thus his co-workers undertook the task of completion in the spirit of his instructions and with all due respect to his scientific legacy.