Energy demand is increasing year by year for both industrial and commercial sectors as well as residential users. In general, several energy carriers, such as electricity, natural gas, thermal energy and/or hydrogen, are required to satisfy end-users' needs. Traditionally, customers make use of these energy carriers without a specific attention on their mutual correlation and integration in a unique system, therefore the energy performance of the global system is not optimized. In a future perspective, improvements in energy infrastructures, new coordinating/control strategies and the development of coupling systems intelligently interconnecting energy carriers are expected to improve the global system efficiency. The studies related to this approach concern on the Energy Hub concept, which is defined as an integrated energy system where several energy sources are used to satisfy the end-user overall energy demand according to a dedicated control strategy. One or more objective functions could be considered, such as gas emission minimization, overall system cost reduction and/or users' comfort maximization. The paper aims at introducing a general modelling and optimization approach to characterize and optimize the energy hub operating conditions. A specific focus on the GHOTEM research project, an Italian program concerning residential study cases considering both old and new buildings, is described.