Smart Product-Service Systems (sPSS) offer the opportunity to create additional value by combining smart products with smart services. However, industry players often lack resources, know-how, and practical guidance to develop, introduce, and maintain such complex solutions. To support their innovation efforts, research first needs to understand the implications of applying these emerging technologies. Hence, we present a maturity model for sPSS to describe and compare such solutions using twelve dimensions and conduct a case study to illustrate the model. Our research combines insights from a systematic literature review, 20 real-world use cases, seven interviews with sPSS experts, and a focus group.