The Dutch government claims that upgrading office buildings to an energy label C building is enough to reduce the environmental footprint of companies for now. Research has shown that when a building receives an energy label, it does not mean that the operational energy use of the building is in line with the received energy label; this results into an energy performance gap. The gap consists of the building-related energy use or the user related energy use. This research focusses on how the behaviour of office users can be influenced to reduce the energy performance of an office building in use. This research is divided into four parts. First the energy performance gap is discussed, afterwards measures which influence the energy performance of an office building are researched, followed by which factors stimulate pro-environmental behaviour and finally which methods are effective to implement the measures and behavioural changes. First, the energy performance gap can be explained by the difference between the theoretical energy label and the operational energy use. There are two possible causes for this gap: the building related energy use or the user related energy use. This research focusses on how to reduce the user-related energy by activating the user behaviour. Secondly, during this study a measurement list is developed to show possible measures to reduce the energy performance and environmental impact of a building. Significant change can be achieved, not by implementing these measures on a small scale (one office), but on a large scale (all offices). It is also the case that these types of measures will not always have a significant effect the environmental impact of the building or the energy use of the building, this depends on the current building characteristics. When a building already implements that measure, the impact will be less significant than when they do not use the measure. Third, pro-environmental behaviour (PEB) is a behaviour type that focusses on minimizing the negative impact of the consequences of human behaviour on the environment (V. Blok et al., 2015). Trough literature, interviews and the delphi panels it can be concluded that comfort, economic and intention play an important role in shaping pro-environmental behaviour (Kollmuss & Agyeman, 2002). The factors which do have the highest impact on encouraging and stimulating Pro-environmental behaviour according to the users and experts are: Intention to act, Perceived behaviour control, Social norms and Eco-communication. Finally, methods to activate these factors are related to the measure and how this measure affects the behaviour factors. In this research three examples of implementing measures are given. The three main methods to reduce the environmental impact of an office building and thereby activating the pro-environmental behaviour of the user are: Pro-environmental behaviour guidelines, Eco- communication platform and Social incentivesCombining the methods will get the optimum result of the measures which are implemented. These four parts combined answers the research question: How can the behaviour of office users be influenced to reduce the energy performance of office buildings in use?