This book reconstructs and discusses the research of Roger J. Williams, exploring the development of his concept of Biochemical Individuality. As a pioneer in the emerging field of biochemistry, Williams examined the biochemical differences among individuals and analyzed how these differences impact science, politics, and society. The analysis traces the evolution of Williams' ideas from inception to conclusion, chronologically reviewing his publications and personal documents from 1919 to 1956. It contextualizes these works within their historical, political, cultural, and scientific frameworks, investigating the terminology, bibliographical data, and scientific content to illustrate how Williams' theories evolved over time, while acknowledging both internal and external influences on this process.