Physics in Common : September 2020　: 　

This is the English version of "Physics in Common" which was written in Japanese some time ago. This textbook should be considreed as a field theory textbook for undergraduate students as well as graduate students. Indeed this book should be the first step toward understanding the textbooks, "Symmetry and Its Breaking in Quantum Field Theory" (Nova Science Publishers, 2011) and "Fundamental Problems in Quantum Field Theory" (Bentham Publishers, 2013).