Energy efficiency feed-in-tariffs (FiTs) are an intriguing new concept for accelerating investment in end-use energy efficiency. By offering a significant new revenue stream for any business that can generate savings, they have the potential to unearth and harness innovations in delivering cost-effective energy savings that have not been seen to date. However, that promise has not yet been tested. Drawing on experience in the United States with related programmes and policies, this white paper identifies, explores and provides recommendations on a variety of design and implementation challenges that will need to be effectively addressed if the potential benefits of efficiency FiTs are to be realized.