This article considers the (il)legality of Crimea's unilateral secession from Ukraine from the perspective of public international law. It examines whether the right to self-determination or an alleged right to (remedial) secession could serve as a legal basis for the separation of the Crimean Peninsula, as the Crimean authorities and the Russian Federation seem to have argued. The article explains that beyond the context of decolonization, the right to self-determination does not encompass a general right to unilateral secession and demonstrates that contemporary international law does not acknowledge a right to remedial secession. With respect to the case of Crimea, it argues that even when assuming that such a right does exist, the threshold in this regard is not met. In the absence of a legal entitlement, the article subsequently turns to the question whether Crimea's unilateral secession was prohibited under international law. It contends that while the principle of territorial integrity discourages unilateral secession, it does not actually prohibit it. Nonetheless, there are situations in which an attempt at unilateral secession is considered to be illegal in view of the circumstances. It is argued that it is precisely this exception that is relevant in the case of Crimea.

In the aftermath of the Ukrainian Revolution, Ukraine’s autonomous region of Crimea declared independence and filed an application to subsequently join the Russian Federation. In seeking to justify these acts, both the Crimean authorities and the Russian Federation referred to international law, including the International Court of Justice’s Advisory Opinion on Kosovo’s unilateral declaration of independence. In this Advisory Opinion, the Court indeed found that the principle of territorial integrity merely applies in the relationship between States and concluded that general international law does not contain a prohibition on unilateral declarations of independence. These findings and the interpretation of the Advisory Opinion as put forward by the Crimean and Russian authorities, however, raise pertinent questions. This article therefore aims to shed light on the scope of the principle of territorial integrity of States and its implications for the legality of and perceived legal neutrality concerning unilateral secession under international law.

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