"Irreversible Phenomena" is a technical book that deals with the theory of thermodynamics and its applications. It illuminates the concepts of ideal and real gases as well as reversible and irreversible processes. The author, Kunio Terao, explains that while ideal states are simple and understandable, they do not exist in reality. The book addresses the second law of thermodynamics and describes how the mathematical formulas applicable to ideal gases can be applied to real gases, provided certain conditions are met. Terao discusses the differences between processes that occur at infinitely low speeds and those that take place at finite speeds, noting that all observed processes in nature are irreversible. This work offers an in-depth analysis of thermodynamic principles and their practical implications.