Industries are transforming their business strategy from a product-centric to a more service-centric nature by bundling products and services into integrated solutions. Such systems which offer value in use are commonly termed Product-Service Systems (PSS) and they tend to enhance the relationship between the provider and their customers. As the research related to Product-Service Systems is currently at a rudimentary stage, the development of a robust ontology for this area would be helpful. The purposes of developing a standardized ontology are that it could help researchers and practitioners to communicate and share their views without ambiguity and thus encourage the conception and implementation of useful methods and tools. In this report, an initial structure of a PSS ontology from the design perspective is proposed and evaluated. The primary objective of this ontology development is to aid clarity to the top-level concepts of PSS which would help to communicate these concepts better between researchers and practitioners. This development included the collection of PSS concepts, the definition of each concept, the grouping and structuring of the concepts hierarchically as well as the identification of the relationships between these concepts. This ontology has been developed from scratch from interviews with experts regarding current practices and challenges within the PSS domain. Some PSS concepts have been extracted from these interviews and structured whilst other concepts have been populated using the PSS literature. Subsequently, the proposed ontology was evaluated by thirty PSS researchers which resulted in revisions and established a common agreement for the structure. Reasoning based on the developed ontology is not within the scope of this work. This ontology could be expanded through multidisciplinary collaborative efforts and should mature as the PSS domain matures.