PREFACE How the Library of the Royal Society of Physicians in Budapest became today’s Semmelweis Medical History Library is a tale of the shift in focus characteristic of the way medical libraries, containing books and journals of contemporary interest and importance to practicing physicians and medical researchers, become medical history libraries over time. This particular library’s story (available previously only in brief and in Hungarian ) is one of just such a transformation and shows what important roles politics, economics, and cultural history can play in whether library materials are preserved and made available to scholars. This account illustrates how establishing and maintaining a library of general medical and (later) medical historical interest requires dedication and generosity on the part of individuals who value medical literature and determine to save it. Many lessons from this case are applicable wherever collections are threatened. Furthermore, the Semmelweis Medical History Library has treasures that medical librarians and scholars elsewhere know too little about: The “Collection of Rarities” comprises more than one thousand volumes, among them incunabula and extremely rare manuscripts in Latin and German, numerous sixteenth-century books, and–beyond medicine and pharmacy–rare books in general history, history of science, natural science, anthropology, and so on. More than three dozen languages are represented.