Our societies and cities must prepare to operate with scarcer and more expensive oil. The most audacious cities have understood that constraints on energy could be a great opportunity to reinvent themselves by relying on another vision of the city of tomorrow: a frugal city, reconciling the satisfaction of citizen needs with an economy of means and resources. Illustrating his point with examples from France and Europe, Jean Haëntjens explains the principles of this model by applying it to the various components of our urban system: mobility, spatial planning, accessibility of utilities, etc.