This chapter describes how the flour milling process interacts with the wheat kernel structure to separate it into its functional components. The chapter traces the historical development of flour milling technology leading to the introduction of roller mills a century ago. It introduces the themes of wheat hardness, bread quality and the international grain trade that brought about modern flour milling. The grinding of wheat into flour is mankind's oldest continuously practised industry and the parent of all modern industry; all modern particle breakage operations have wheat milling in their ancestry. The “golden rule” of the flour miller is to maintain consistent flour quality, as consistency of raw materials is the baker's number one priority. In pursuing this goal, the major tool employed by the miller is blending of different wheats together, known as gristing. The breakage equation for roller milling of wheat allows the effects of a constantly changing feedstock to be predicted and controlled.