In this talk I will present concepts of the terrestrial carbon budget, such as gross primary production, respiration, and disturbance and management fluxes, and its consequence on the annual growth rate of atmospheric CO2 concentration. In doing so, I will also present main observational and modelling methods to estimate the terrestrial carbon budget from ecosystem to global scale. Then, I will focus on current spatial pattern of the component fluxes as well as their recent time evolution. I will particularly also point to the important links to carbon and nutrient cycles. The main part of the talk will then concentrate on the potential responses of the carbon land-atmosphere exchanges to environmental change. This envolves a review of the carbon stocks and quality distribution, and a review on processes that can alter a current balance, such as consequences of energy limitation of microbes on decomposition or thawing of permanently frozen soil organic matter. Such altered carbon budget an land surface properties can lead to feedbacks with the climate system. I will also address the question of effects of a changing climate variability in comparison to a changing average of a climatic variable on terrestrial ecosystem state and function.