Articles are presented, covering a wide range of topics in the mathematical methods of quantum physics. These include infinite dimensional analysis based on white noise, operator algebra methods, Feynman path integrals, quantum mechanics on non-simply connected spaces, recent results in supersymmetric theories, stochastic and quantum dynamics, Yang-Baxter systems, statistical physics, thermo field dynamics, and quantum field theory.The essays are based on lectures contributed for the Second Jagna International Workshop held in honour of Prof. Hiroshi Ezawa, a distinguished physicist, educator, and former president of the Physical Society of Japan.