In a world of increasing atmospheric CO2, there is intensified interest in the ecophysiology of photosynthesis and increasing attention is being given to carbon exchange and storage in natural ecosystems. We need to know how much photosynthesis of terrestrial and aquatic vegetation will change as global CO2 increases. Are there major ecosystems, such as the boreal forests, which may become important sinks of CO2 and slow down the effects of anthropogenic CO2 emissions on climate? Will the composition of the vegetation change as a result of CO2 increase?This volume reviews the progress which has been made in understanding photosynthesis in the past few decades at several levels of integration from the molecular level to canopy, ecosystem and global scales.