The field of quantum chemistry has grown so immensely that the importance of some of the earliest work and the earliest pioneers of quantum chemistry is unfamiliar to many of today's youngest scientists in the field. Thus, this book is an attempt to preserve some of the very valuable, early history of quantum chemistry, providing the reader with not only a perspective of the science, but a perspective of the early pioneers themselves, some of whom were quite interesting characters. The symposium on which this book is based came about because one of the co-editors (ETS) came to a conviction that the contributions such as those by George Wheland to quantum chemistry and Otto Schmidt to free electron theory should be better appreciated and known. He organized a symposium in which quantum chemistry pioneers, both those celebrated by everyone and those seemingly overlooked by posterity, would be recognized. While this volume is certainly not a history of quantum chemistry, it does cover many highlights over a period of about sixty years. This volume consists of chapters based upon ten of the presentations at the symposium "Pioneers of Quantum Chemistry" held March 28, 2011, at the 241st ACS National Meeting in Anaheim, CA.