In its Advisory Opinion of 22 July 2010, the International Court of Justice concluded that the declaration of independence in respect of Kosovo in its precise historical circumstances "did not violate any applicable rule of international law". In its reasoning, the Opinion is concerned with territorial integrity, self-determination and Security Council competence under Chapter VII UN Charter. The Court’s Opinion – its reasoning and outcome – can be assessed from several angles. Adopting instead the perspective of legal theory, our concern will be what we can learn from the Opinion about the normative structure of international law in general, and as applied in the context of secessions in a non-colonial context. The paper will argue that the approach of the International Court of Justice to international law, as evidenced in the case at hand, may be labeled rule-oriented. After reconstructing the main planks of the Court’s reasoning, the paper will set out an alternative conceptual framework, arguing for a shift from a rule-centered to a principle-based approach to international law in the interest of legal certainty. It will then explore what room there is for such an approach to secessionist situations based on the understanding of self-determination as principle.