Technical Abstract: Switchgrass (Panicum virgatum L.) is an important bioenergy crop with the potential to provide a reliable supply of renewable energy while also removing CO2 from the atmosphere and sequestering it in the soil. The purpose of this study was to use micrometeorological techniques to quantify CO2 fluxes during the establishment and early production years of a young switchgrass stand in the northeastern USA. ‘Cave-N-Rock’ switchgrass was established in June, 2004, and daily carbon dioxide fluxes were measured from 1 October 2004 to 30 September 2008. Biomass produced each summer was allowed to overwinter in the field and was harvested just before new growth began the next spring. Gross primary productivity (GPP) varied little among years, ranging from -3355 to -3451 g CO2 m-2 yr-1. However, ecosystem respiration (Re) decreased over time from 3339 g CO2 m-2 yr-1 in 2004-2005 to 2661 g CO2 m-2 yr-1 in 2007-2008. The ecosystem generally began to take up CO2 in Mid-May and continued until early-October, and was a net sink during a 98-day period from late-May through early-September. The rest of the year experienced a net loss of CO2 to the atmosphere. Harvested biomass increased each year and was not correlated with GPP. The system was a net CO2 sink for the first three years, but became a source the final year due to increased removal of C as harvested biomass. This study suggests that in addition to their primary function as a source of renewable energy, switchgrass bioenergy crops in the northeastern USA can sequester CO2 for the first few years following establishment.