Is there something important to learn from the history of science about knowledge and the mind? Do habits and emotions play a significant role in science? To what extent do present concerns and knowledge distort our understanding of past texts and practices? These are crucial questions in current debates, but they are not new. This monograph evaluates the answers to these and other questions that Hélène Metzger (1889-1944) provided. Metzger, who was the leading historian of chemistry of her generation, left us unparalleled reflections on the theory, practice and aims of history writing. Despite her influence on subsequent generations of thinkers, including Thomas Kuhn, this is the first full-length monograph on her. Beginning with an overview of her life, and the challenges faced by a Jewish woman working within academia, the book goes on to discuss the most important themes of her historiography, and her engagement with other disciplines, notably general history, philosophy, ethnology and religious studies. The book also explores both Metzger's immediate legacy and the relevance of her ideas for a host of current debates in science studies. The Appendices include four of her historiographical papers, translated into English for the first time.