This report presents some approaches to modelize urban energy systems. More precisely, as a first step, a clear definition of what is an urban energy system model is exposed before listing the main tech- niques of modelization. With the goal to run a case study, two of these techniques are developed, the technology design and the system design. The latter is characterized by the use of optimization tools, which are briefly explained. Softwares like OSMOSE are run thanks to optimization methods, that is why the decomposition of an opti- mization sequence and then the software itself are presented. Finally, the theoretical part of this report is closed by the introduction of a central notion when modelizing and optimizing urban energy systems, the pinch analysis. The second part of the present report illustrates the use of the tools and concepts seen by then through a case study. Playing with two conflictive objectives, OSMOSE is run to find the best trade off for the example of the Meyrin Site, exploited by the CERN.