In New York, the energy used in buildings is a major source of pollution, accounting for about 75 percent of the city’s overall greenhouse gas emissions. In 2007, soot emitted by New York City buildings burning residual fuel oil – No. 4 and No. 6 oils – caused more fine particulate pollution than all of the vehicles on the city’s streets combined. To combat this, the New York City Department of Environmental Protection issued regulations requiring that buildings convert to cleaner fuels from heavy heating oil beginning in July 2012. But because of perceived market hurdles, the deadline for some of the dirty fuels stretched out to 2030. This case study tells the story of how the City of New York, EDF, and other partners worked to overcome these barriers by creating the NYC Clean Heat program, which led to one of the fastest and most significant air quality improvements in New York City history. The campaign united action by government, utilities, banks, real estate leaders, and non-profits to help buildings convert their boilers to a range of cleaner options, including natural gas, ultra-low sulfur No. 2 oil, and biodiesel.