This document discusses the need for companies transitioning to product-service systems to define modular service offerings that can be provided across multiple product lines. It proposes a new method for defining service modules that consist of standardized services that can be leveraged for different products. The method builds on existing research on product modularity and platforms to extend the concept of modularity to integrated product-service systems. Defining modular services could help companies provide standardized service offerings more efficiently at scale, similar to how product modularity enables variety through reusable product modules.