This study focuses on the theoretical background of the genre of alternative history, and aims to introduce the concept and characteristics, varieties, and historical strategies of allohistoricism. In a separate section, the paper discusses the oldest works itemizable as allohistorical, dating back to the works of Herodotus and Titus Livius. As the study aims to provide a system of criteria for the examination of alternative historical works—first and foremost novels—, it considers its basic task to be the processing of the most significant Anglo-Saxon and the complete Hungarian literature on the subject. The list of the existing approaches and the reasoning systems following from the definitions of the integrated special literature, and those of our own analysis and categorization, will outline a pattern that can be used repeatedly in the future in analyses focusing on the individual works.