This manual provides guidance and best practices on how to use data for developing and implementing policy on building energy efficiency. The primary audience for this manual are the C40 cities in the Private Building Efficiency (PBE) network and the Municipal Building Efficiency (MBE) network. Most of the guidance is applicable to both PBE and MBE networks. Where guidance is specific to PBE or MBE, it is called out accordingly. The users of the manual include city policy makers, efficiency program administrators and data analysts as well as external consultants supporting them.