Sidney Coleman was a physicist's physicist. He is largely unknown outside of the theoretical physics community, and known only by reputation to the younger generation. He was an unusually effective teacher, famed for his wit, his insight and his encyclopedic knowledge of the field to which he made many important contributions. There are many first-rate quantum field theory books (the venerable Bjorken and Drell, the more modern Itzykson and Zuber, the now-standard Peskin and Schroeder, and the recent Zee), but the immediacy of Prof. Coleman's approach and his ability to present an argument simply without sacrificing rigor makes his book easy to read and ideal for the student. Part of the motivation in producing this book is to pass on the work of this outstanding physicist to later generations, a record of his teaching that he was too busy to leave himself. Readership: Graduate students and academics interested in quantum field theory. "Sidney Coleman was the master teacher of quantum field theory. All of us who knew him became his students and disciples. Sidney s legendary course remains fresh and bracing, because he chose his topics with a sure feel for the essential, and treated them with elegant economy." -- Frank Wilczek, Nobel Laureate in Physics 2004 "When stumped on some physics, I often still ask myself, even after nearly forty years, 'What would Sidney say?' His lectures and their transcriptions were models of clarity and charm. The subjects remain crucial to frontier physics. This volume is a treasure." -- Hugh David Politzer, Nobel Laureate in Physics 2004 "Ah, quantum field theory: through Coleman's eyes we watch a victory parade that made 'the spectator gasp with awe and laugh with joy'!" -- Anthony Zee, University of California, Santa Barbara and author of Quantum Field Theory in a Nutshell "Sidney Coleman's course on quantum field theory was one of the most memorable and enjoyable experiences of my physics education. Uniquely meticulous and insightful, these notes from his lectures will be invaluable to anyone interested in the cornerstone topic of modern physics." -- Sean Carroll, Caltech and author of Spacetime and Geometry: An Introduction to General Relativity "Sidney Coleman's Field Theory lectures at Harvard were a staple of every particle physicist Harvard graduate student's education … the ideas like all good physics concepts have survived the decades beautifully. In a labor of love and educational devotion, a team of former students and TAs teamed up with professors and experts to share his legacy in perpetuity." -- Lisa Randall, Harvard "It may seem strange to refer to a book on Quantum Field Theory as 'fun' but this book is fun. The reader not only sees important physics and math, but also gets to appreciate a Master Teacher at work. It is wonderful to have these lectures written down so that they can be pored over and savored multiple times. David Politzer said it best in the acknowledgment in his Nobel-Prize-winning thesis on asymptotic freedom. 'To Sidney Coleman my teacher and advisor, who with his cleverness and cunning, conned me into thinking that good physics is simple, I am forever indebted … Thanks to him, my understanding of field theory has never been so clear, but sometimes my head feels funny.'" -- Howard Georgi, Harvard "Ah, quantum field theory: through Coleman's eyes we watch a victory parade that made 'the spectator gasp with awe and laugh with joy'!" -- Anthony Zee, University of California, Santa Barbara and author of Quantum Field Theory in a Nutshell "Sidney Coleman's course on quantum field theory was one of the most memorable and enjoyable experiences of my physics education. Uniquely meticulous and insightful, these notes from his lectures will be invaluable to anyone interested in the cornerstone topic of modern physics." -- Sean Carroll, Caltech and author of Spacetime and Geometry: An Introduction to General Relativity "Sidney Coleman's Field Theory lectures at Harvard were a staple of every particle physicist Harvard graduate student's education ... the ideas — like all good physics concepts — have survived the decades beautifully. In a labor of love and educational devotion, a team of former students and TAs teamed up with professors and experts to share his legacy in perpetuity." -- Lisa Randall, Harvard "It may seem strange to refer to a book on Quantum Field Theory as 'fun' — but this book is fun. The reader not only sees important physics and math, but also gets to appreciate a Master Teacher at work. It is wonderful to have these lectures written down so that they can be pored over and savored multiple times. David Politzer said it best in the acknowledgment in his Nobel-Prize-winning thesis on asymptotic freedom. 'To Sidney Coleman my teacher and advisor, who with his cleverness and cunning, conned me into thinking that good physics is simple, I am forever indebted … Thanks to him, my understanding of field theory has nev