This book had its genesis in a conference (of which Moshe Lewin was the principal organiser) that took place in Philadelphia in September 1991. Fifty scholars from five countries – France, Germany, Russia, the United Kingdom, and the United States – took part. The aim of the conference was to explore similarities and differences in the development of Russia and Germany during the twentieth century. The Cold War had not encouraged comparison outside the framework of the totalitarianism concept and its assumption that comparison assumed similarity. The conference accepted no such imperative and ranged across the century, tackling a broad array of topics – some widely couched, others more narrowly focused – that reached back into the monarchical systems before the First World War and forward to the demise of the Soviet system. The wide thematic and chronological range of the comparison, the conceptual framework of the enquiry, and the fact that it could take place without the ritual ideological posturing which had existed in the era of the Cold War, meant that the conference was breaking new ground. The participants shared the view that comparison offered the nearest the historian could come to the laboratory experiment of the natural scientist, but that there is no single prescribed or specific method to undertake comparative history. The methods and approaches must remain eclectic and pragmatic in comparative history, as in any other kind of historical analysis.