Two types of barriers are responsible for the low adoption behaviour in the domain of energy efficiency. Barriers that are external to the decision maker and mainly depend on institutional settings. These are capital market failures, information problems, as well as financial and technological risks. Second, internal barriers that cannot be easily changed, because they relate to preferences and behaviour. A new report has been produced within the PENNY project, with a dual objective. First it discusses how internal and external barriers influence energy efficiency choices. Second it analyses which policies and interventions proved to be most effective in addressing the specific barriers, and result in higher adoption and more pro-environment energy use.