Lactose has been commercially produced since the early part of the twentieth century. Worldwide production increased phenomenally in the 1940s when it was found that lactose was the best substrate for penicillin production. Further increases in lactose production resulted when mothers started to use infant formula, which contains lactose as the major constituent. Late in the twentieth century, confectioners found many reasons to use crystalline lactose in chocolates. Today chocolates are second only to infant formulae as the major use of lactose. In this presentation, the author shares some of his 40 years of experience operating and designing commercial-scale lactose production systems. Each unit operation for lactose production is discussed with a focus of how each unit operation can affect lactose quality and yield. The following unit operations are covered: raw material supply, concentration (RO and evaporation), crystallization, refining, drying and packaging. Particular attention will be given to the current state of the art, which is not typically covered in various textbooks. Finally, a review of traditional and new methods for producing pharmaceutical grade lactose are discussed.