Cities are responsible for 65% of energy consumption and for the 70% of CO2 emissions. Incisive actions are fundamental to bring cities towards climate neutrality by 2050 working by and for the citizens. For this reason, the “100 climate-neutral cities Mission” anticipates the target of climate neutrality by 2030. The objective of this paper, developed within the H2020 GRETA project—GReen Energy Transition Actions (GA101022317), is to investigate energy communities and climate city contracts as key interventions to face the ambitious goal of implementing citizens-centered and climate-neutral cities. To achieve this objective, this paper is structured as follows: (1) an updated framework of European and Italian legislation concerning energy communities; (2) an overview of climate city contracts’ definition and key aspects; (3) a selection and analysis of energy communities’ case studies; (4) a description of already developed pilot climate city contracts. The results provide more advanced knowledge about EU energy communities strategies and about the possible contractual agreements that can guarantee commitment between parties and can allow the active participation of citizens in the energy system. The lessons learned contribute to the application in the GRETA Italian case study, whose first participation activities are also described in the paper.