The microstructure of superalloys is highly complex, with a large number of dispersed intermetallics and other phases that modify alloy behavior through their composition, morphology, and distribution. This chapter provides an overview of the most notable phases, including the matrix phase and geometrically and topologically close-packed phases, and describes how superalloy microstructure can be modified via heat treatments and directional solidification. It also discusses the role of carbides, borides, oxides, and nitrides and the detrimental effects of sulfocarbides.