This paper is intended to provide a scoping review on interfaces in service modularity. There is little detailed understanding of this concept despite its attributed importance. We identified 12 papers, showing that interfaces in service modularity are an area still open to research, especially with regard to interfaces that cross organisational boundaries. We found common themes in the available literature: the nature of interfaces, service fragmentation and predefined interfaces. Further research is needed on interfaces in service modularity, especially for complex services with components that stem from multiple, autonomous organisations. More specifically, there is a need for more studies that explore in detail how interfaces manifest themselves, and how they can be addressed to improve complex service provision. In addition, we argue why healthcare could be an interesting domain in which to conduct those studies. Our paper's contribution comprises a detailed description of interfaces in service modularity, the dissemination of summarised research findings and suggestions for potential future research.