"For anyone interested in the rapidly developing field of string theory (graduate students with the proper physics background), Siegel's book is a particularly good introduction.">/p> Choice, USA "Siegel has played a major role in the application of BRST formalisms for quantization to string theory … Siegel's book is of great interest for those who intend to do research in string field theory." Foundations of Physics, USA This volume covers the most up-to-date findings on string field theory. It is presented in a new approach as a result of insights gained from the theory. This includes the use of a universal method for treating free field theories, which allows the derivation of a single, simple, free, local, Poincare-invariant, gauge-invariant action that can be applied directly to any fields.