Forests cover about thirty percent of the Earth’s land surface and are important in providing critical ecosystem services, including carbon sequestration, storage, and cycling. Forests sequester and store more carbon than any other terrestrial ecosystem on Earth. In forests, plants take up carbon dioxide from the atmosphere and release oxygen during photosynthesis, which transfers carbon to their stems, roots, and leaves as they grow. Forests store carbon in five major pools, these are: i) aboveground biomass, ii) belowground biomass, iii) litter, iv) deadwood and v) soil. Forests are also a major source of global anthropogenic carbon emissions, the second largest after fossil fuel. Protecting forests from deforestation and degradation and expansion of forest in new areas is, therefore, considered as amongst the most cost-effective strategy for climate change mitigation. Here, we provide a synthesis of current knowledge regarding forest carbon stock and fluxes, their distribution across different biomes, biogeochemical cycles, their measurement and drivers of change in global forest carbon stock and fluxes. Finally, we provide recommendations on strategies for improving forest carbon stocks to achieve sustainable development goals, biodiversity conservation, and future climate stabilization.