In this paper, we review 20 relatively recent empirical studies of telecommuting, all of which focus on the trip reduction perspective. The studies include earlier ones with smaller datasets, such assome pilot studies of individual employers, and more recent studies based on broader surveys of both telecommuters and nontelecommuters. We focus on the results of the studies with respect to participationand frequency of telecommuting, the effects on vehicle-miles-traveled (VMT) and trips, and in some cases, the impacts on emissions and air quality. Although there does not seem to be a consensus, there is apredominant view that certain factors increase both the likelihood of telecommuting and the frequency of telecommuting. These factors are having children in the household, being female, having more education,having a longer commute trip, having worked longer for one’s current employer and/or in one’s current position, and having a job that does not require face-to-face contact with coworkers or clients. Moststudies of VMT and trip reductions from telecommuting show that telecommuters significantly reduce both daily trips and VMT. Not only does commute VMT fall, but noncommute VMT appears to fall insome cases as well. The studies of VMT, however, tend to focus on the reductions for individual employees who choose to telecommute. Although an individual telecommuter may experience a sharpreduction in VMT, total benefits depend on how many people are telecommuting, how often they are doing so, and the duration of telecommuting. More research is needed with larger and more broadly based datasets across employers that include both individual employee characteristics and employer and job characteristics. This would allow a better analysis of telecommuting choice and frequency as well as more reliable estimates of VMT and emissions impacts.This discussion paper is one in a series of four RFF papers on telecommuting published in December 2004. Discussion papers 04-42 and 04-43 present analyses of two recent datasets on telecommuters. In 04-42, Nelson and Walls analyze data from five pilot cities enrolled in the "ecommute" program. In 04-43, Safirova and Walls analyze data from a broad survey conducted by the Southern California Association of Governments (SCAG) of telecommuters and nontelecommuters. Finally, in 04-45 Nelson presents an assessment of institutional and regulatory barriers to using telecommuting in a mobile source emissions trading program. 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/.