Natural gas energy efficiency programs offered by utilities and related organizations have been in place in many states for 30 or more years. These programs provide incentives and services that assist customers in making improvements and investments in energy efficiency to reduce energy costs. The number of states where such programs are provided to natural gas customers has grown steadily. Budgets for programs have grown rapidly in recent years as utilities strive to achieve high savings. ACEEE surveyed state regulators and program staff to complete a national review of natural gas efficiency programs. The research also draws upon data available from other national organizations. This report examines the structure, origins, funding, and impacts of natural gas efficiency programs for the forty-one states where they are in place. It traces funding trends and examines the impacts of recent policy innovations, particularly “energy efficiency resource standards.”