In line with EU Directives, European building portfolio owners are required to bring their stock to nearly Zero Energy Building (nZEB) standards by 2050. To fulfil this goal in a timely and cost-effective manner, they will need to have a comprehensive understanding of their buildings’ condition, as well as consistent information on viable energy and low-carbon technology measures. Currently, in Europe, there is a lack of knowledge of what energy efficiency measures are being implemented in residential buildings. It is also unknown what are the decision-making processes behind the selection of these measures. On this basis, the aim of this study is to shed light on (1) what energy efficiency measures are currently carried out across European building portfolio owners (BPOs), (2) how are these measures selected (i.e. decisionmaking processes and information sources), and (3) what data would be needed to foster the uptake of low carbon energy efficiency technologies. The applied methodology combines desk research on scientific and grey literature, with findings in the field of building maintenance & operation. The later based on semi-structured interviews with 23 selected private and public BPOs across 7 European countries: Sweden, UK, Germany, Denmark, Italy, Spain and Switzerland. Results show that the most often implemented actions are the maintenance of the roof and the upgrade of the heating system. Measures are decided based on a combined planned and “reactive” (i.e. problem/solution) approach. The data that is typically used by BPOs is basic building information, such as gross floor area or year built. Although currently unavailable, the most often solicited evidence by the BPOS in favour of energy efficiency and low carbon technology measures is related to energy consumption and other user data.