Foreword of those rare the interesting than the theoretical game itself.Nevertheless,he delighted in theoretical physics and in its teaching.a subject on which he held strong opinions.He thought that much theoretical physics teaching was both too na ..we see a number of so cated.vet uneducated.theoreticians who ars comversant in the Lsphisti for malism of the Heisenberg field operators,but do not know why an excited atom radiates.or are ignorant of the quantum theoretic derivation of Rayleigh's law that acco nts for the bluer ess of the sky."And he insisted that the nt use what has been taught ."The e rea der who has read the book but cannot do the exercises has learned nothing. He put these principles to work in his fine book Advanced Ouantum chamics (1967and in Invariamce Principles and Elementary Particles (1964),both of which have beer used in the CERN library. This new book,Modern Quantum Mechanics,should be used even more,by a larger and less specialized group.The book combines breadth of interest with a thorough practicality.Its readers will find here what they need to know,with a sustained and successful effort to make it intelligible. J.J.Sakurai' sudden death on November 1,1982 left this book unfinished.Reinhold Bertlmann and I helped Mrs.Sakurai sort out her husband's papers at CERN.Among them we found a rough,handwritten version of most of the book and a la e collection of exercis s.Though only three chapters had been completely finished.it was clear that the bulk of the creative work had been done.It was also clear that much work remained to fill in gaps,polish the writing.and put the manuscript in order. That the book is now finished is due to the determination of noriko Sakurai and the dedication of San Fu Tuan.Upon her husband's death Mrs.Sakurai resolved immediately that his last effort should not go to waste.With great courage and dignity she became the driving force behind the project,overcoming all obstacles and setting the high standards to be maintai ined.San Fu Tuan willingly gave his tim and er nergy to the editing completion of Sakurai's work.Perhaps on others cl e to the hectic field of high-energy theoretical physics can fully appreciate the sacrifice involved. For me rsonally,J.J.had long been far more than just a particu larly distingu It saddens me that we will never again laugh together at physics and physicists and life in general,and that he will not see the success of his last work.But I am happy that it has been brought to fruition. John S.Bell CERN,Geneva