The global environment is changing with increasing temperature and atmospheric carbon dioxide concentration, [CO2]. Because these two factors are concomitant, and the global [CO2] rise will affect all biomes across the full global range of temperatures, it is essential to review the theory and observations on effects of temperature and [CO2] interactions on plant carbon balance, growth, development, biomass accumulation and yield. Although there are sound theoretical reasons for expecting a larger stimulation of net CO2 assimilation rates by increased [CO2] at higher temperatures, this does not necessarily mean that the pattern of biomass and yield responses to increasing [CO2] and temperature is determined by this response. This paper reviews the interactions between the effects of [CO2] and temperature on plants. There is little unequivocal evidence for large differences in response to [CO2] at different temperatures, as studies are confounded by the different responses of species adapted and acclimated to different temperatures, and the interspecific differences in growth form and development pattern. We conclude by stressing the importance of initiation and expansion of meristems and organs and the balance between assimilate supply and sink activity in determining the growth response to increasing [CO2] and temperature.