In 1999 Congress passed the National Air Quality and Telecommuting Act. This Act established pilot telecommuting programs in five major U.S. metropolitan areas with the express purpose of studying the feasibility of addressing air quality concerns through telecommuting. This study provides the first analysis of data from the "ecommute" program. Using two-and-one-half years of data, we look at telecommuting frequency, mode choice, and emissions reductions. We also look at reporting behavior, dropout rates, and other information to assess the program's performance. We analyze results by city- Denver, Washington, D.C., Houston, Los Angeles, and Philadelphia are the five pilot cities. And finally, we use the program's emissions reduction findings to calculate how much telecommuting would be needed to reach an annual volatile organic compounds emission reduction target in each city. This discussion paper is one in a series of four RFF papers on telecommuting published in December 2004. In addition to analysis of the ecommute data described in this paper, Safirova and Walls (discussion paper 04-43) similarly analyze data from a 2002 survey conducted by the Southern California Association of Governments (SCAG) of telecommuters and nontelecommuters. These same authors put these findings into context by providing a review of the empirical literature on telecommuting (discussion paper 04-44). Finally, Nelson presents an assessment of institutional and regulatory barriers to using telecommuting in a mobile source emissions trading program (04-45). The studies by RFF are part of a larger report on the ecommute program completed by the Global Environment and Technology Foundation (GETF) for the U.S. Environmental Protection Agency. More information about the overall project can be found on the ecommute/GETF website: http://www.ecommute.net/program/.