Few IR studies are dedicated to the concept of non-intervention, frequently equated with states' sovereignty-deduced right to independence. This thesis investigates how (non)intervention, understood as a set of discursive formations revolving around the idea of forcible external (non)interference in the internal affairs of a polity, emerged and evolved from the Peace of Westphalia to present. This contribution draws on an abductively selected body of discourses (treaties and legal documents, the doctrine, and the discourses of statesmen and representatives) within four historical European junctures (the Westphalian moment, the Revolutionary era, the Concert of Europe, and the post-Cold War period), to undertake a discursive analysis of (non)intervention by analysing objects, statements, systems of concepts, themes and rules for four defining elements of (non)intervention (conceptions of authority and sovereignty, their scope (jurisdiction of sovereignty), relations between peer polities, and rules for the use of force). Drawing on these analyses, this thesis demonstrates that 1) the principle of non-intervention was not related to early (‘Westphalian’) conceptions of sovereignty, and that its meanings and understandings rather fluctuated over time; 2) for centuries simultaneously held conceptions of non-intervention and intervention were not perceived as paradoxical and co-existed both in the doctrine and in the political realm; 3) the principle of non-intervention has been codified recently, from the mid-nineteenth century, and more universally in 1945 with the UN Charter, but it represent an abrupt shift for precedent practices and adherence to it is still largely contested in the political realm.