Product Service Systems (PSS) are increasingly important for companies. They enable a multitude of advantages, including the ability to offer customers even more individual customised solutions. However, PSS can also cause negative effects for companies. For example, PSS increase the complexity within companies. In order to cope with this complexity, the modularisation of PSS is frequently suggested in literature. However, existing approaches for modularisation only consider functional reasons for module composition and neglect the product-strategic aspects. This paper introduces a new approach for the modularisation of PSS, which combines functional and product-strategic aspects into one approach. To achieve this, a separate modular structure is developed for each life phase. Following this, these are harmonised across all life phases. This enables the advantages of the modular PSS structure to be used in all life phases. A PSS family of laser processing machines is used to illustrate the new developed approach.