Recognizing the importance of the existence and role of megacities in contemporary societies, the subject thesis aims to analyze the core aspects of the rapid growth of megacities, including both qualitative and quantitative data, with regard to the concepts of sustainability and geopolitics. In this scope, a descriptive analysis of the most outstanding sustainability metrics and calculation formulas is present in this thesis, accompanied by specific measures and policies undertaken and implemented in different case studies. The thorough analysis of the available bibliography regarding megacities and sustainability is followed by a geopolitical review, with specific reference to the challenges detected within and among megacities, as well as to the advantageous practices adopted by them. Additionally, a questionnaire has been created for the purpose of the present thesis, addressed to a focal group of experts, whose outcomes are demonstrated and discussed, providing a more representable and unambiguous depiction of the correlation between megacities, sustainability and geopolitics. Finally, a series of recommendations and incentives for further research and advancement of the current endeavor are also part of this thesis, constituting a useful ground for further research.