The volume demonstrates that the modeling of tree and forest growth based on physiological processes is emerging as an important discipline in forestry research. Some possible directions for future research include the development of overall carbon budgets with maintenance and growth respiration considered separately, the development of a comparative (across species) approach in modeling, and the further analysis of the relationship between the processes of growth and those of mortality and reproduction. A long-term goal of the modeling effort should be to reduce the number of assumptions used in the models and increase the number of calculated or predicted results.