In this master thesis, a methodology for the estimation of electrical energy demand of buildings using a 3D city model is presented. The idea of include that kind of data lies in the fact that nowadays those models are rich of geometric and semantical data, which could be useful in energy demand forecasting. The first part of the document introduces the basic concepts of the Geographic Information Systems, the CityGML standard and the Web Map Services. As well as the introduction of basic concepts of energy and the presentation of several methods for the estimation of electrical energy demand. After the presentation of the different methodologies, the selection of the End-Use method is done, which is the one that better suits the scope of this master thesis. After the selection of the method to use, a better presentation of its characteristics is done. Later the comprehensive tools for processing CityGML files are presented, giving a description of their characteristics and why are they considered. After this chapter the problem statement of the master thesis is done. In the following chapter the methodology for the estimation of electrical energy demand is done, first from a theoretical perspective being detailed in every single step of the process at the end the chapter is concluded by the presentation of the work-flow diagram that better states the ideas presented. After this chapter the results of an area of study used in the implementation part of the master thesis are shown, in this section the methodology is evaluated and some adjustments to the initial idea are done. The final chapter of this document is dedicated to the conclusions and the presentation of further researches that could take place after.