Many state policymakers and utility regulators have established aggressive energy efficiency (EE) savings targets which will necessitate investing billions of dollars in existing buildings - and tax payer and utility bill payer funding is a small fraction of the total investment needed. Given this challenge, some EE program administrators are exploring ways to increase their reliance on financing with the aim of amplifying the impact of limited program monies. While financing is potentially an attractive tool for increasing program leverage and mitigating the rate impacts of utility customer-funded efficiency programs, administrators can face difficult choices between allocating funds to financing or to other approaches designed to overcome a broader set of barriers to consumer investment in EE. Robust assessments of financing's role in reducing energy use in buildings are necessary to help policymakers and program administrators make better choices about how to allocate limited resources to achieve cost effective energy savings at scale. In order to better understand what EE financing can be reasonably expected to achieve, and for whom, this book is organized around three levels of inquiry (Figure 1), from the most fundamental (level 1) to the most detailed (level 3).