There are many uncertainties in the role of forest ecosystems in slowing down the increases of atmospheric carbon dioxide concentration and their responses to and feedbacks on the global change associated with the increasing CO2 concentration in the atmosphere and the global increase in nitrogen deposition. Research on the interactions and coupling of carbon and nitrogen cycling in forest ecosystems can pinpoint and thus reduce these uncertainties. Such studies also improve the understanding of the relationships between the productivity and nutrient cycling in forest ecosystems and mechanisms for sustaining the long-term site productivity. The coupling between carbon and nitrogen cycles in forest ecosystems includes photosynthetic processes, autotrophic respiration process, decomposition process of litter and soil organic matter, fine root turnover process, and heterotrophic respiration process. Both positive and negative feedback mechanisms and nonlinear relationships are involved in these processes, which ultimately determine the carbon balance in forest ecosystems. This paper reviews the current literature on the coupling functions between carbon and nitrogen cycles, and describes recent advances, existing shortcomings and limitations of research in this area. The directions for future research in this area are also discussed.