The largest part of the European ports are engaged into addressing proactively environmental and societal issues in order to achieve an always more sustainable development. However, there are several sources that indicate that gaps and barriers exist which impede the sustainable development of many Mediterranean ports. In order to deal with the problems that are identified in ports and specifically in container terminals, which are closely related to their sustainable performance, a framework is developed. The creation of the Port Sustainability Assessment Framework (PSAF) allows the comparison of the current state of terminals with the desired state based on specific sustainability themes and consequently, evaluates their performance. Port sustainability is also approached by means of stakeholders' views and insights, throughout a questionnaire. The application of the framework in the case studies of Piraeus and Livorno, two container terminals of different sizes and challenges but both located in the Mediterranean area, proves that the concept of sustainability in the two container terminal case studies has not yet been embedded in the planning and operational phase as their sustainable performance is low. Another aspect that this master thesis addresses is the need to extend the Port of the Future Serious Game (PoFSG) in order to include in a realistic way port-city future developments and their potential impacts on the environment and the society, as well as to facilitate stakeholder engagement. Based on the results of the sustainability assessment, several weaknesses of the PoFSG are identified and tools are developed which can be useful for extending the PoFSG. The focus is mostly drawn upon two specific aspects: the scoring system of the measures' performance on “People, Planet and Profit” and the inclusion of relevant sustainability measures. Additionally, more general recommendations are made for the other aspects of the PoFSG.