Professor Kimball Milton is the George Lynn Cross Research Professor of Physics at the University of Oklahoma. Kim Milton, a student of Julian Schwinger, studies in particular vacuum energy phenomena (the Casimir effect) in contexts ranging from cosmological through hadronic to condensed matter systems. He is the author, together with J Mehra of "Climbing the Mountain: The Scientific Biography of Julian Schwinger" Oxford University Press, 2000.

"The main goal of this short book is to examine quantum action principles and, in particular, the Schwinger action principle. ... For anyone who is interested in a good but brief introduction to the subject, this monograph should be considered." (Paul F. Bracken, Mathematical Reviews, April, 2016)

• Historical introduction.- Review of classical action principles.- Classical field theory - electrodynamics.- Quantum Action Principle.- Time-cycle or Schwinger-keldysh Formulation.- Relativistic Theory of Fields.- Nonrelativistic Source theory.- Concluding remarks.

Professor Kimball Milton is the George Lynn Cross Research Professor of Physics at the University of Oklahoma. Kim Milton, a student of Julian Schwinger, studies in particular vacuum energy phenomena (the Casimir effect) in contexts ranging from cosmological through hadronic to condensed matter systems. He is the author, together with J Mehra of "Climbing the Mountain: The Scientific Biography of Julian Schwinger" Oxford University Press, 2000.

"The main goal of this short book is to examine quantum action principles and, in particular, the Schwinger action principle. ... For anyone who is interested in a good but brief introduction to the subject, this monograph should be considered." (Paul F. Bracken, Mathematical Reviews, April, 2016)

• Historical introduction.- Review of classical action principles.- Classical field theory - electrodynamics.- Quantum Action Principle.- Time-cycle or Schwinger-keldysh Formulation.- Relativistic Theory of Fields.- Nonrelativistic Source theory.- Concluding remarks.

Professor Kimball Milton is the George Lynn Cross Research Professor of Physics at the University of Oklahoma. Kim Milton, a student of Julian Schwinger, studies in particular vacuum energy phenomena (the Casimir effect) in contexts ranging from cosmological through hadronic to condensed matter systems. He is the author, together with J Mehra of "Climbing the Mountain: The Scientific Biography of Julian Schwinger" Oxford University Press, 2000.

"The main goal of this short book is to examine quantum action principles and, in particular, the Schwinger action principle. ... For anyone who is interested in a good but brief introduction to the subject, this monograph should be considered." (Paul F. Bracken, Mathematical Reviews, April, 2016)

• Historical introduction.- Review of classical action principles.- Classical field theory - electrodynamics.- Quantum Action Principle.- Time-cycle or Schwinger-keldysh Formulation.- Relativistic Theory of Fields.- Nonrelativistic Source theory.- Concluding remarks.