With dramatic fluctuations in feed, fuel, and fertilizer prices, much attention is again being paid toward use of cover crops in agricultural systems. Cover crops provide benefits to agricultural systems such as reductions nitrogen (N) loss and potential reduction in N fertilizer need to maintain crop yields. Cover crops in Wisconsin’s agricultural systems are most often used prior to corn following a short season crop such as winter wheat, potatoes, or vegetables. There are two main types of cover crops used in Wisconsin: (1) cool-season grasses and (2) legumes. Cool-season grasses are primarily used to provide ground cover in cropping systems that leave little residue after harvest in effort to reduce soil erosion. Leguminous cover crops are used to add N into the soil system through biological fixation of atmospheric N. When these legumes are incorporated into the soil, this “fixed” N becomes plant available as the soil tissue decomposes. Legume crops are grown for one season or less, and incorporated into the soil without harvesting, are referred to as green manures. Current UW recommendations are to take N credits when utilizing green manures such as alfalfa, sweet clover, red clover, and hairy vetch (Table 1). However, several field studies conducted in the past decade indicate that cool-season grasses and other green manures such as berseem clover, crimson clover, and medic also impact the economic optimum N fertilizer rate (i.e., the N fertilizer rate that maximizes the economic return to N based on the price ratio of N fertilizer and corn). This paper summarizes recent research related to both cover crop types in Wisconsin.