Seasonal changes in forage productivity and nutritive value will influence pasture management and ration balancing decisions by the producer.  We determined seasonal yield and quality changes in the leaf and stem fraction of 10 temperate perennial grasses at two Wisconsin locations.  After reaching 6 in. height in the spring, summer, and fall, Kentucky bluegrass, ryegrass, orchardgrass, timothy, tall fescue (conventional and soft-leaf), meadow fescue, smooth bromegrass, reed canarygrass, and quackgrass were harvested to a 4 in. stubble every 5 days to 30 days maturity.  Leaf and stem yield were greater in northern than southern Wisconsin during the spring and summer, and similar in fall.  Kentucky bluegrass and smooth bromegrass were the most productive in the spring at both locations at 20 days of maturity (mean of 1500 lb leaf and 800 lb stem DM/acre at approximately 8 and 12 in. height, respectively).  Perennial ryegrass was the least productive at both locations (mean of 800 lb DM/acre), but produced little or no stem fraction.  Greatest yield was produced in the summer and fall by both tall fescues (1000 to 2000 lb DM/acre).  Leaf and stem crude protein (CP) were greater in northern than southern Wisconsin during the spring (difference of 3 to 5%).  Leaf CP of all grasses except Kentucky bluegrass and tall fescue generally remained above 20% up to 20 days maturity in all seasons.  Neutral detergent fiber (cell wall) digestibility (NDFD) of all grasses was greatest in the spring (mean of 70%) and lowest in summer (mean of 60%) at both locations.  Greatest NDFD was measured in the spring in ryegrass and in the fall in meadow fescue.  Timing of grazing is most critical for Kentucky bluegrass, reed canarygrass, and tall fescue, particularly in spring and summer, due to rapid declines in digestibility with maturity.