The research presented in this thesis demonstrates the qualitative modelling of an advanced service delivered by a Product Service System (PSS) through the use of a socio-technical systems-based approach. The created model represents dependencies between functions and organisations, and can be used as basis for a quantitative cost model. Focus is on how one particular example of advanced services, namely availability is delivered in an industrial context. Following a review of multi-disciplinary literature and the outline of a suitable methodological approach, a detailed case study of the delivery of an exemplar piece of avionics equipment by BAE Systems and GE Aviation to the UK Royal Air Force is described. This research shows that the delivery of avionics availability through a PSS has organisational, contractual and functional facets that overlap and influence each other. Multiple qualitative models represent the investigated setting, from a functional and from an organisational perspective. Top-level functions ‘Analysis & Optimisation’, ‘Administration’ and ‘Delivery’ are identified. The results show distinctive similarities and differences between GE Aviation and BAE Systems including a variety of parallel contracts, organisational segmentation and tensions between relationships and contractual obligations. The findings suggest that understanding a PSS as a socio-technical system is crucial for modelling the PSS and the cost associated with it. This is particularly important when the aim is to continuously control and manage costs rather than the creation of a one-off forecast. The contribution of this work to the existing body of knowledge, primarily within the domain of cost engineering is twofold: First the creation of qualitative models of an existing PSS delivering avionics availability to show “what is a PSS”, and second a methodologically robust approach that takes into account the sociotechnical character of PSS to demonstrate “how to know about PSS”