Grazing management has a significant impact on pasture growth.  We determined how timing of grazing influences grass productivity, yield distribution, and persistence.  Meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.], orchardgrass (Dactylis glomerata L.), quackgrass [Elymus repens (L.) Gould], and reed canarygrass (Phalaris arundinacea L.) were grazed in the spring (early May), summer (late July), or fall (late September) with dairy heifers when grasses reached 15-, 30- (control), and 45-cm height to a 5- to 8-cm residual height.  During the remainder of the season, grasses were grazed at a 30-cm height to an 8-cm residual height.  Yield and nutritive value of grazed herbage were measured at each grazing event.  Tiller density was measured after two years.  Grazing at 15 cm in the spring reduced yield but had little effect on productivity during the remainder of the year compared to grazing at a control height.  Similar yields were produced by grazing at 15 and 30 cm in the summer, but productivity during the remainder of the year was reduced by grazing at 15 cm.  Grazing at 45 cm during the spring increased annual yield, but not during the summer and fall, and increased the proportion of herbage produced during the treatment period.  Herbage nutritive value was negatively impacted only by grazing at 45 cm.  Persistence of all grasses except orchardgrass was reduced 20 to 40% by grazing at 15 cm during the summer.  Grazing at 15 cm height during the summer had the greatest negative impact on grass productivity and persistence.