In recent years, there is growing evidence that global warming arises from human activities, and as a result, efforts are being made worldwide to ease the burden on the environment and avoid the worst consequences of climate change. One of the most important interventions is the decrease in carbon emissions from the energy sector. In the Cyclades islands there is still a very large margin for improvement, especially considering the great potential from renewable energy sources, such as wind and solar. While there have been relevant studies for some of these islands, there is not a complete plan for the transition towards sustainable energy. Therefore, a backcasting analysis is used in this thesis in order to answer the main research question: How can a sustainable energy system in the Cyclades islands be realised by 2030? While there is a lot of ground to be covered in the transition, the slightly short end-point of 2030 is chosen, also to align with the policies of the Greek state. It is envisioned that the energy system by then shall be sustainable, self-sufficient, efficient, and reliable. After developing the energy mix for each island, a “What-Who-How” backcasting analysis is conducted as part of the backcasting framework, in order to identify the full extent of the necessary interventions. The chief change towards the transition is of course the installation of renewable energy projects, and other, supporting systems, while the development of a strong policy framework is also a key requirement. Moreover, it is important that the public is also included in the transition, educated, and informed. Also, it is worth noting that further attention is being placed on the accommodation sector, owing to its considerable effect brought on by the touristic character of the islands. Based on the identified actions and interventions, an implementation timeline is developed until the end-point of 2030. The transition is split into three phases, each with a specific goal in mind. In the beginning, the first steps and the preparation for the future will be made, while afterwards the system will be ready to be functioning with the generation of energy by RES. Finally, in the third phase the storage of energy will also be available and the transition will thus be complete. Overall, transitioning to a sustainable energy system in the Cyclades is technically feasible. Nevertheless, there are quite a large number of both technical and non-technical changes necessary, and they need to be carried out in a rather short amount of time if the target of 2030 is to be attained. It is understandable therefore that a strong policy framework and a keen cooperation between the stakeholders are of utmost importance, in order for the Cyclades to have a sustainable energy system by 2030.