The microstructure of sintered materials is typically described by two physically measurable state variables: relative density and average grain size. However, these parameters alone are insufficient to fully capture the complexity of pore structures that develop during the actual sintering process. This chapter presents case studies on how raw powder characteristics and processing methods influence the detailed microstructure of green bodies. It also describes how these heterogeneous green bodies either evolve into uniform, dense materials through sintering or give rise to defect formation.