An international workshop on `CO₂ and Biosphere' was held in Wageningen, the Netherlands on 15-19 November 1991 as part of the activities of the CO₂ Commission of the Netherlands Organization for Scientific Research: this volume includes 32 papers presented at the workshop. The CO₂ Commission stimulates and coordinates a broad range of research projects related to the greenhouse effect. This is reflected in the scope of papers presented, ranging from detailed analyses of ecological and physiological effects of atmospheric CO₂ enrichment to biosphere-atmosphere aspects, such as regional evaporation, energy balance and ecosystem responses. Relevant directions for future research are indicated by presentations on carbon fluxes in the soil, secondary plant metabolism and plant-insect interactions.