This chapter focuses on (1) clay transport within the soil profile and (2) the dynamics of soil organic matter, of which soil carbon is the most important component. Clay and soil organic matter combine in the soil profile and are a major driver of the soil structure evolution (the clay-organic complexes) and soil structure is a major influence on the infiltration rate of rainfall into the soil. There is a strong relationship between soil carbon content and soil water holding capacity. Soil organic matter consists of compounds containing carbon, phosphorus, nitrogen and sulphur. Operational models for the evolution of soil organic matter typically model the cycles of these elements but in this chapter we will only consider soil organic matter (SOM) in total, or the carbon component of it, soil organic carbon (SOC). SOM contains 58% SOC in units of mass C/mass soil. SOM contains particulate organics, humus, charcoal, living microbes, root exudates, fungi, and fine plant roots. The living biomass (the vast majority of which is microbes and fungi) is a major influence on the decomposition of dead organic matter and the storage of carbon and nutrients.