Switchgrass (Panicum virgatum) is a highly regarded potential lignocellulosic biomass crop. The objective of this study was to determine the relative importance of yield components on biomass production at different developmental stages during the growing season.Cultivars of switchgrass in seeded trials were harvested for biomass and yield component determinations at monthly intervals during 2005 and 2006. Data collected were biomass, tillers per m2, mass per tiller, phytomers per tiller, and mass per phytomer. Data were analyzed with stepwise multiple linear regression, and path coefficients were calculated to determine the relative importance of each yield component in determining biomass production. Path coefficient values of yield components varied with harvest date, developmental stage, location, and cultivar. Direct effects (i.e., path coefficients) of yield components were generally larger for tillers per m2 than for mass per tiller, phytomers per tiller, or mass per phytomer. However, direct effects of mass per tiller were larger than for tillers per m2 in several high-biomass-yield environments. Coefficients of determination varied from 0.59 to 0.97, indicating the multiple linear regression yield component model explained most of the variation in biomass yield.