Many organisations are moving from mass production to mass customization. Product configuration systems (PCS) are increasingly seen as an interesting option for firms who wish to pursue a strategy with a high degree of product variance while retaining a low cost of specifying the product. To become more specific in relation to how product configuration systems can support mass customization, it is necessary to understand how different product configuration systems can be classified, and how these differ. This paper presents a typology of product configuration systems based on the five kinds of knowledge needed for the configuration task. Lastly, we discuss the implementation and use-related issues that can be derived from the typology.