Mass customisation aims at best satisfying individual customer needs with near mass production efficiency. Due to the diversity of individual customer needs, the number of possible unique product offerings can be astronomical. Meanwhile, there can be many potential production process alternatives for each unique product. The compounding effects of product and process proliferation can significantly escalate the production cost and can impose additional delays. In order to cater to diverse individual customers' requirements without adversely affecting the production cost and delivery, this paper develops a systematic approach to manage the product and process variety, based on which economies of scale can be achieved through sharing the commonalities of components, tooling, operations and expertise. The approach organises the knowledge of product variety through Generic Bills-of-Materials (GBOM) and process variety through Master Process (MP). Matching matrices are constructed to manage the relationships between them. A case study is presented to illustrate the approach.