This article examines how aspirant states with limited international recognition secure membership in international organisations. While soft and control power is a suitable framework to explore the foreign policy conduct of recognised states, in this article, we argue that aspirant states facing significant barriers to full recognition and membership in international organisations can leverage protean power, which involves adaptability, strategic innovation, and improvisation, to navigate complex political landscapes and achieve varying degrees of success in their pursuit of international legitimacy. We use Kosovo's diplomatic efforts as a case study, examining its successes and failures in joining organisations such as the World Customs Organization, the Permanent Court of Arbitration, and UNESCO. By comparing successful, partially successful, and unsuccessful cases, the article provides critical insights into the dynamics of international legitimacy, the politicisation of multilateral decision-making, and the evolving norms of state membership in a fragmented international order.