Preface to the Revised Edition Since 1989 the Editor has enthusiastically pursued a revised edition of Modern Quantum Mechanics by his late great friend J.J.Sakurai,in order to extend this text's usefulness into the twenty-first century.Much con- sultation took plac with the panel of Sakurai friendswho elped with the original edition,but in partic lar with Professor Yasuo Hara of Tsukuba University and Professor Akio Sakurai of Kyoto Sangyo University in Japan. The major motivation for this project is to rvisc the main text There are three important additions and/or changes to th vised edition which otherwise preserves the original version unchanged.These include a reworking of certain portions of Section 5.2 on time-independent per- turbation theory for the degenerate case by Professor Kenneth Johnson of M.I.T.,taking into account a subtle poin ot that ha snot been properly treated by a number of texts on quantum mechanics in this country.Professor Roger Newton of Indiana University contributed refinements on lifetime broadening in Stark effect,additional explanations of phase shifts at res- onances,the optical theorem,and on non-normalizable state.These appear as"rem arks by the edito or edit r's note in the revised editi fessor Thomas Fulton of the Johns Hopkins University reworked his Cou- lomb Scattering contribution (Section 7.13)so that it now appears as a shorter text portion emphasizing the physics,with the mathematical details relegated to Though not a major part of the text,some additions were deemed necessary to take into account developments in quantum mechanics that have become prominent since November 1,1982.To this end,two sup- mare inded at the end of the text.Supplementison a nge and rical phase (popularized by M.V.Berry since 1983) and is actually an English translation of the supplement on this subjec written by Professor Akio Sakurai for the Japanese version of Modern Quantum Mechanics(copyright Yoshioka-Shoten Publishing of Kyoto) pplement II is on nor onential decays written by my colleague here or Xerxe ata,and over by rofessor E. G.Sudar shan of the University of Texas at Austin.Though non-exponential decays have a long history theoretically,experimental work on transition rates that tests indirectly such decays was donc only in 1990.Introduction of additional material is of co urs subjectiv matter on the part of the Editor;the readers will evaluate for themselves its appropriateness.Thanks to Pro- fessor Akio Sakurai,the revised edition has been "finely toothcombed' for misprint errors of the first ten printings of the original edition.My colleague,Professor Sandip Pakvasa,provided overall guidance and en- couragement to me throughout this process of revision