In this chapter we will try to bring the best possible answers to these two questions without entering into much scientific complexity, but at the same time avoiding oversimplification. We will start with some definitions and explanation of terms. To determine the existing C stocks by vegetation type we will present the respective area and C content per hectare of each vegetation type. Then to have an estimation of past and present human activities, we will give estimates of deforestation and degradation linked to agriculture, forestry (logging) and other land uses. We will briefly expose the state of knowledge about C fluxes through ecological processes and what we can reasonably deduce for Congo Basin forests. Finally we will conclude with a note of caution describing the uncertainties in the estimations presented in this chapter.