The provision of services has become an increasingly important component of the economy of industrialized countries and the revenue stream for many traditional product companies. This is especially true for companies that offer information technology (IT) products. This paper examines factors that are associated with the extent to which IT product companies are able to develop service revenue, which we refer to as service expansion of IT product companies. We identify the characteristics of the product portfolio-specifically, the composition and scope of firm offerings among hardware, application software, and infrastructure software-as key to successful service expansion. We also propose that this relationship is moderated by prior performance of the product business and industry characteristics such as concentration and maturity. Data from IT product vendors spanning five years are used to test the proposed relationships. Overall, this research provides a theoretical foundation for understanding service expansion and diversification in the IT industry as well as practical guidance for IT product companies considering expansion to services.Key wordS and phraSeS: IT services, IT stack, IT vendors, service diversification, software product portfolio. SErVIcE EXPANSION OF PrODucT FIrMS IN ThE IT INDuSTrY 129service businesses complement each other-that is, design feedback obtained from services can provide strategic direction for product development, while the integration of serviceable components into products can enable new services. In summary, these studies have focused on service expansion as a management action (independent variable) and examined the resulting consequences for firms. Despite these arguments identifying the advantages of service expansion for product companies, little research has explored the organizational drivers of successful service expansion, making this an open area for research. An implicit assumption is that IT product vendors provide services to exploit their existing competencies, especially the competencies accumulated through the product business [82]. however, no research has explored the specific competencies that enable or motivate these firms to expand their offerings to include services.The goal of this research is to identify the factors that enable product firms to successfully expand their service offerings. We consider product companies providing services as an expansion into a new but related line of business, such that knowledge and resources from the existing product business are relevant to understanding the new service business [50, 51,71,94]. 1 This suggests that the product portfolios of IT vendors are likely to be a key enabler of service expansion, as vendors with different product portfolios will have different knowledge resources [51, 72]. We focus on two kinds of knowledge resources-customer knowledge and architectural knowledgebecause they are critical to the provision of services. We further suggest that a stack framework, which includes layers (from bottom ...