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.