The chapter examines the reasons for, and two dominant responses to, the diversity of world views that underpin contemporary international relations (IR) theory. The first response, conquest, opposes diversity and seeks to privilege one particular worldview. The second response, coexistence, is one that finds no good reason to privilege a particular worldview, and attributes a positive value to diversity and pluralism. The chapter distinguishes between two dimensions of a worldview and distinguishes between worldviews and theories. It also provides an historical overview to account for the proliferation of worldviews in the field and the lack of consensus regarding the appropriate criteria for comparing and evaluating the merits of competing worldviews. Finally, the chapter sets out the main arguments associated with conquest and coexistence between worldviews, and defends the case for the latter.