For the last 5 years, research has been undertaken on associations of coffee and shade trees in Central America to promote coffee agroforestry systems in the region and to improve coffee farmers' incomes through diversification (timber production), production of high quality coffee and payment of incentives for environmental services in order to compensate for the low coffee prices of recent years. Field measurements have been undertaken to study and model partitioning of light, nutrients and water between coffee and trees, and impacts of shade trees on microclimate, coffee physiology and quality. Farm surveys have also been done to study farmer coffee agroforestry practices and changes in agricultural management in face of the persistent coffee crisis. These results show that shade creates more favorable microclimatic conditions for coffee cultivation by decreasing leaf temperature of up to 4°C under sub-optimal conditions of low altitude (< 700 m) and by up to 2°C under optimal conditions (> 1100 m). Under sub-optimal conditions, the presence of shade trees reduces coffee heat stress, enhances coffee growth and productivity with an adequate shade level in the range of 20-40%. These results also show that coffee transpiration is lower under shade trees (Eucalyptus deglupta or Terminalia ivorensis) or artificial shade than in full sun. These results demonstrate that beneficial effects of shade are not limited to sub-optimal conditions as the presence of shade improves coffee quality, irrespective of the ecological conditions, via a lengthening of the maturation period of coffee berries (up to 6 weeks under shade trees in sub-optimal conditions, and up to 3-4 weeks under artificial shade in optimal conditions). This translates into better bean filling, larger bean size, improved biochemical composition and higher cup quality. Coffee beverage from sun-grown coffee is bitter and more astringent than that from shade-grown ones. Furthermore, beverage acidity and pr