Under suboptimal site condition for arabica coffee cultivation the shade trees increase the coffee production due to an enhancement of the microclimate and the soil fertility. Under optimal site conditions, the use of shade are more controversial, nevertheless the agroforestry systems (AFS) provide others services as the reduction of erosion and the diversification of production. The present study compare in optimal site conditions in Costa Rica a coffee monoculture (MC) and AFS with Inga densiflora Benth in terms of microclimate, productivity and water balance. In reference to MC, the shade trees reduced the global radiation between 40% to 50%, the maximal coffee leaf temperature to 6°C, the leaf to air VPD during the day and increased the leaf temperature in 0.5°C during night. According to the year of measurement, the trees increased the rainfall interception (12% to 85%) and the total system transpiration (29% to 33%), at the same time trees reduced the runoff (50%) and the drainage (1% to 14%). The trees reduced the throughfall, increased the stemflow and contributed 40% to 50% to the total transpiration of the AFS reducing the coffee transpiration in the AFS. Furthermore, higher reductions in the AFS compared to MC in soil water in deeper soil layers indicate a complementarity interaction in the use of water between coffee and trees. Despite the absence of water competition under these site conditions, the coffee yield was reduced by 29% in the AFS in comparison to the MC, due to a reduction in the radiation and flowering intensity. In other hand, the total aerial biomass was 3 times in the AFS compared to MC, contributing to carbon sequestration and renewable energy.