Résumé : The joint development agreements allow states to jointly explore and exploit the potential and proved hydrocarbon reserves in the disputed areas, without giving up their sovereignty claims. It is widely used in many areas around the world from the South China Sea to West Africa. States explore, produce and create economic gains from the resources in disputed areas. However, despite the mentioned benefits, states with disputed maritime claims do not always sign joint development agreements or not all attempts succeed. In this thesis, I have analysed the following research question: Why did the joint development agreement proposal fail in Cyprus? Previous literature has limited works on the failure of the joint development proposals. This thesis aimed to contribute to the joint development and the Cyprus literature by arguing the determinants of the failure and success of joint development agreements. Regarding the ongoing dispute between two communities of the island, increasing tension due to the oil and gas exploration operations and the refused joint development proposal in Cyprus in July 2019, I selected the Cyprus case for the research. I have applied the combined rationalist theoretical approach to explain the failure, combining the structural constraints and capability distribution concepts from the neorealist approach with expected economic gains concept from neoliberalism. Adapting the theoretical concepts to the case, I have measured the influence of the regional powers on the failure through increasing the unilateral operational capabilities of the communities and the role of expected economic gains on the failure. I have used discourse analysis method to measure to what extent the mentioned factors can be observed in the discourses of the key actors. In addition to the discourses of the top officials from the Cypriot communities, I analysed discourses from several other parties such as the EU, Egypt, Israel and Turkey. While the findings confirmed the effect of the regional powers on the failure of the proposal by increasing the unilateral operational capabilities of the communities, the hypothesis of expected economic gains only partially supported. Discourses highlighted the EU’s influence on the failure by increasing the unilateral operational capability of the Greek Cypriots through European oil companies, diplomatic support and transportation projects. Egypt and Israel shifted the Greek unilateral capabilities by diplomacy and transportation projects. Turkey limited the technical capability and controlled maritime area of the Greek side while enhancing the regional support of the Greek Cypriots because of the strained relations with Egypt and Israel.