This thesis focuses on advancing the digitization of socio-technical energy systems by facilitating the creation of Digital Twins of Energy Communities (ECs). A multi-layered architectural model was proposed to capture the different domains and interconnections within multi-energy and multi-agent ECs. Leveraging this framework, a flexible and modular co-simulation platform was realised as a tool that can be employed for enhancing research, decision-making, and policy analysis. Three study cases showcased the platform's capability to represent different ownership topologies, energy trading mechanisms and agents and control strategies. The study cases demonstrated that the holistic design and customisability of the platform allow for representing nuances and capturing cross-layer effects, thus unlocking a deeper understanding of ECs' dynamics and their members' outcomes.