The Netherlands Council for Environment and Infrastructure (RLI) is working on energy recommendations in which it explores how a fully sustainable energy system can be achieved by the year 2050. A key issue in this context is how energy demand and CO2 emissions will develop through to 2050 for the four basic energy functions of light/appliances, transport/mobility, and high- and low-temperature heat. Distinguishing between these four functions is particularly relevant when analysing future trends, because despite all the uncertainties about the future, the need for these functions will continue to exist. By proceeding from functionalities rather than sectors (as is generally the case), it is easier to disengage from the present state of affairs and analyse future developments.