This chapter describes carbon flux field data that can be used to parameterize and validate models that couple biophysics, ecophysiology, biogeochemistry, and ecosystem dynamics. The intent of these models is to understand how the carbon balances of forests ecosystems respond to their environment and disturbances on multiple time-scales. The chapter also describes the carbon balance of deciduous broadleaved forests in temperate zones and in the adjacent Mediterranean zones of the world. It examines the processes controlling net and gross carbon exchange information at the scale of the canopy. The chapter discusses the dynamics of carbon exchange components of temperate forests on hourly, daily, and annual time-scales. The net amount of carbon that a forest ecosystem is able to acquire over the course of a year is called net ecosystem productivity. The respiratory costs of supporting the light-harvesting superstructure must be less than the ability of the system to harvest light energy, in the form of carbon.