Customizing offerings to match customers’ specific needs is a common practice for manufacturers striving to maintain their competence in markets. Despite Product/Service Systems (PSSs) having developed substantially in industry and academia for the last two decades, no scientific review of PSS customization has been published. This prompted us to conduct a review of scientific papers relating to products, services, and PSS customization with a focus on design, with the aim of clarifying future research directions in PSS customization. In particular, distinct design models and methods were individually examined, with a special focus on service aspects, in terms of what to design and how to design it. The population of papers included in the review was those included in the Web of Science. Even though service customization has been utilizing the knowledge generated by product customization, which has been researched extensively for decades, there are differences between them, such as the difficulty associated with modularity. The same or even larger differences apply to PSS customization, because, apart from service characteristics, PSS also has product characteristics and thus is more complex. Results also include that the module-based platform strategy used in service customization can also be used for PSS. Although several papers concerned with PSS customization have been published thus far, their focus has been on the service aspect of PSS, providing further research opportunities. Existing methods to design PSS can be also applied to develop a method for PSS customization.