Multigeneration (MG) of different energy vectors, such as electricity, heat, cooling, and others, represents a viable alternative to improve energy generation efficiencyand decrease the environmental burden of energy systems. In particular, trigeneration plants can be efficiently deployed to supply complex energy services inurban areas, with typically high heat demand of heat in winter and different levels ofcooling demand throughout the year, depending on the specific application. MG couldbe applied through a number of solutions exploiting for instance generators for smallscaledistributed CHP (combined heat and power, or cogeneration), heat-fired absorptionchillers, electrical heat pumps, and so forth. Managing MG systems is a challengingtask due to the energy flow interactions among the manifold pieces of equipment withinthe plant and with external energy networks. In addition, different objectives could bepursued, for instance of economic, technical, or environmental nature, or a combinationof the above. Therefore, robust methodologies for MG optimisation are needed, to copewith most general cases. In this context, this chapter presents a comprehensive introductionto modeling, analysis, and assessment of MG systems in the operational timeframe, with special focus to cogeneration and trigeneration. It is shown how to formulate, in a compact and systematic form, suitable operational optimisation problems of differentkinds. In particular, also relying upon relevant literature recently published in thefield, the main variables involved in the analysis and the complexity of the operationaloptimization problem formulations and solutions are highlighted, including how tohandle possible conflicting objectives within multiobjective optimization and relevantsolution approaches.