This thesis analyses the energy performance of dense cities and residential towers. It focuses on the energy performance of the built environment at three different scales – the building, the façade and the city area. The details of the three “morpho-energetic” studies are as follows : 1 - the first one analyses the link between buildings' dimensions and their energy performance: it focuses on a simple calculation method to quickly approximate the whole energy balance of residential buildings. 2 - the second study analyses the morphology of energy and density reasoned city areas: the ultimate goal is to develop a tool helping to find the optimal form(s) of a low energy and dense city area. It is based on a genetic algorithm tool. 3 - the last one analyses the energy impact of a new design methodology for construction and refurbishment: the Core-Skin-Shell concept.