This chapter focuses on the dynamics of soil organic C (SOC) in the carbon (C) cycle in grasslands. Recent years have seen much discussion of the potential impact of altered environmental conditions on storage of C in grasslands and other natural ecosystems (Parton et al., 1995; Ojima 1993 a, b; Hunt et al., 1991; VEMAP, 1995). This chapter discusses how potential changes in climatic factors like precipitation and air temperature, induced by greenhouse gases, may alter C dynamics in grasslands, and it considers the effect of increased atmospheric CO2 and the combined effect of increased CO2 and altered climatic conditions.