This chapter provides a framework for the companion by defining world crime fiction and outlining the key theoretical issues involved in studying crime fiction as a global genre. The first section explores the global and transnational prehistories of crime fiction; it covers various forms of premodern crime writing and discusses the global dissemination of Western crime fiction from the late nineteenth century, highlighting the role of translation, pseudotranslation and adaptation in the emergence of local crime literatures. The second section focusses on the transnationalism of contemporary world crime fiction, arguing that the global adaptations of the genre are not just a matter of adding local colour, but involve formal hybridization that results in new, local versions of the genre. The final section discusses how crime fiction studies, as a field traditionally tied to Western crime writing, has recently moved towards a global and transnational conception of the genre. The overarching argument of the chapter is that founding world crime fiction as a research area requires a rethinking of the crime genre itself beyond the Anglocentrism of the scholarly tradition.