## 1 Introduction  
Urbanization is a major global trend, with the United Nations [1] forecasting that 68% of the world population will reside in urban areas by 2050, up from 30% in 1950. This shift highlights the need for efficient urban planning, particularly in the transportation sector, which is vital for urban development. Private vehicles, a primary mode of transport, contribute significantly to CO, CO\({}_{2}\), and NH\({}_{3}\) emissions [2]. To improve urban sustainability and to push toward greener mobility, the European Commission has implemented initiatives such as the Sustainable Development Goals (SDG) and the \"Fit for 55 in 2030\" project. In particular, they aim to reduce these emissions, to promote decarbonization of the transportation sector, and to encourage the transition to electric vehicles (EVs).  
In the decarbonization perspective, the introduction of electric vehicles will play an increasingly important role, creating a growing challenge to the energy supply in the appropriate areas. However, the vision of electric vehicles as the only consumers of energy is limiting. In fact, the growing demand of electricity can cause issues to grid stability, in particular, in the peak hours. The vehicle-to-grid (V2G) technology of EVs has thus recently gained interest as a clean and green energy and has opened new opportunities for EV owners [3]. The new challenges are to enable electric vehicles to participate in the electricity market as active customers who can feed the electricity stored in EV batteries back to the power grid during peak hours to help balance the growing demand for electricity and avoid the need for grid investments. In fact, the V2G paradigm proposes the use of vehicle batteries not only as energy accumulators but also as energy suppliers according to the needs of the entire electricity grid, making electric vehicles active participants in energy management [4, 5]. This approach is of particular interest if it is considered that electric vehicles, predominantly used for systematic short daily trips, such as home-to-work or home-to-school commutes, often store and keep significant amounts of electricity unused during long parking periods [6, 7, 8, 9, 10]. Therefore, the current research is focused on exploring how to exploit this unused energy and its potential contribution to the power grid. It aims to consider electric vehicles not only as passive accumulators but also as active energy providers, integrated into the dynamic and bidirectional management of electricity.  
As a result, the purpose of this work is to explore the current literature in order to point out the status of the research and the fields that need to be further developed in order to support the real implementation of V2G. It will focus on the ecological transitions to sustainability, travel characteristics, technical specifications, requirements, and barriers in real use, and the behavioral and psychological aspects of stakeholders. In fact, although some review studies have been proposed on this topic, they mainly focus on technological aspects and barriers with little emphasis on user needs and expectations [11, 12, 13, 14].  
The rest of the paper is organized as follows. Section 2 introduces the systematic literature review methodology, while Section 3 presents the application of the methodology to the research field identified above and the results obtained. Finally, the conclusions and the road ahead are drawn in Section 4.