Climate change often seems like a distant threat that is not directly connected to our daily lives. However, everyday consumer behaviour is an important determinant of sustainability. The EU-funded project 'Policy addressing climate change and learning about consumer behaviour and everyday life' (PACHELBEL) worked on assisting policymaking to understand and facilitate consumer behaviour that favours sustainability. Looking closely at citizen engagement as a policy tool to support governance, trust and legitimacy, the project team engaged with policymakers and lay citizens to study the linkages between them. The project worked rigorously on developing the new policymaking support tool and guiding policymakers on how to use it. Such a tool would be capable of revealing citizens' culturally shaped behaviours related to sustainability, and highlighting how citizens rationalised these behaviours. Through extensive active research efforts and reconvened and reflective discussion groups with citizens, the project team designed a prototype for the tool and tested it in different real-world situations to find the best ways of providing suitable policymaking support. In addition to the design, development and operationalisation of the policymaking support tool, the project team produced valuable guidance on how best to use the tool across a range of policy environments. In each country within the project's scope, the team cooperated with policymakers to identify a current policy issue of interest or to validate knowledge about citizens' sustainability-related behaviours. These specific policy issues were investigated with specially recruited groups of citizens using the methodology developed within the project. A key policy issue explored, for example, was related to energy use, including electricity consumption and the use of smart meters. The resulting tool (STAVE: Systematic Tool for Behavioral Assumption Validation and Exploration) can reveal the nature of practical barriers preventing the adoption of environmental-friendly consumer behaviours. The tool offers a means to allow policymakers to design and communicate their sustainability policies much more effectively. The feedback received from the collaborating policy organizations was overwhelmingly positive. Overall, the project has created a user-friendly support tool that rapidly generates accurate data about everyday citizen behaviour, thus yielding information that can be used in a wide range of policy contexts. Trials have been conducted in six European countries, demonstrating the tool's viability. Dissemination of PACHELBEL results has been supported by the project website, publications and conference presentations. This tool could well play a pivotal role in promoting sustainability and mitigating the effects of climate change.