International law faces impetus for epistemic and disciplinary change. This is manifest in today’s policymaking and academic context, where the term ‘interdisciplinary’ can be seen everywhere, ranging from funding calls, research agendas, grant applications, conference themes and internet blogs to rhetorical manoeuvres. The traditional certainty of knowledge divided between exclusive domains of scholarly specialization, it is alleged, no longer holds. For international lawyers this grinds against a commonsense division of scholarly labour tied to what historical sociology calls perceived ‘objective qualities’ of professions, such that treaties and cases belong objectively to international lawyers similar to how the notion of space intuitively triggers associations with geographers (earth), physicists (matter) and even astronomers (outer space or cosmology). Yet, perceptions of how knowledge is ordered and produced have evolved considerably over centuries, both in conceptual and social terms. As such, the purpose of this chapter is to explain to international lawyers how interdisciplinarity is neither a choice nor a label owned by a particular scholarly agenda, but rather a historical and strategic reality of the still evolving conceptual, institutional and political map of knowledge ordering.