Wheat quality derives from interactions between the components of the kernel. In turn these components are themselves collections of multiple sub-components. Many components are under genetic control and are modulated, if not profoundly influenced, by growing conditions. This chapter focuses on the three main polymeric components of wheat grain: protein, starch, and fibre, as these are arguably the primary contributors to wheat flour functionality. It explores the relationship between sustainable wheat production and wheat grain quality and milling performance as well as analysing in detail the protein, starch and fibre composition of wheat grain.