Symbiotic association between forage legumes and N₂-fixing microorganisms reduces the need for pasture N fertilization and increases forage N concentration. Pastures of cool-season legumes mixed with annual ryegrass (Lolium multiflorum Lam.) are an option to extend the grazing season in subtropical regions. We investigated the association of 4 cool-season legumes with annual ryegrass and contrasted with annual ryegrass in monoculture. Clovers tested included balansa (Trifolium michelianum Savi), ball (Trifolium nigrescens Viv.), berseem (Trifolium alexandrinum L.), and crimson (Trifolium incarnatum L.). Treatments were replicated 4 times in a randomized complete block design. Response variables analyzed included total dry matter yield (DMY), clover DMY, annual ryegrass DMY, ¹⁵N grass, ¹⁵N legume, botanical composition, N concentration of grass and legume components, shoot N yield for grass and legume, percentage of N derived from atmosphere (%Ndfa), and N₂-fixation by the legume. Legume/annual ryegrass mixtures yielded more biomass (average of 2,590 kg DM ha⁻¹) compared with unfertilized annual ryegrass (980 kg DM ha⁻¹). Among mixtures, crimson clover/annual ryegrass was the most (P < 0.01) productive one (4,580 kg DM ha⁻¹). Crimson (2,230 kg DM ha⁻¹) and berseem (1,720 DM ha⁻¹) clovers were the 2 most productive legumes. Annual ryegrass yielded more biomass (P < 0.001) when mixed with crimson clover compared with other clover mixtures. Clover percentage in the mixtures ranged from 26 to 74%, with berseem showing the highest proportion. Total shoot N yields were 29, 41, 49, 88, and 11 kg N ha⁻¹ for balansa, ball, berseem, crimson, and unfertilized ryegrass, respectively. The %Ndfa for all clovers were high, varying from 67 to 98%. N₂-fixation ranged from 11 to 52 kg N ha⁻¹, with crimson fixing the greatest amount. Crimson clover presented the best overall performance when mixed with annual ryegrass in North Florida.