This book presents the derivation of the fluctuation theorems with divergent entropy production and their application to fundamental problems in statistical physics. It explores the two basic aspects of the fluctuation theorems: i) Applicability in extreme situations with divergent entropy production, concluding that the fluctuation theorems remain valid under the notion of absolute irreversibility, and ii) utility in the investigation of classical enigmas in the framework of statistical physics, i.e., Gibbs and Loschmidt paradoxes. The book offers readers an overview of the research in fundamental statistical physics. Firstly it briefly but skillfully reviews the modern development of fluctuation theorems to found the key theme of the book. Secondly it concisely discusses historical issues of statistical physics in chronological order, along with the key literature in the field. They help readers easily follow the key developments in the fundamental research of statistical physics.