The study addresses the design of Product-Service Systems (PSSs) as a means of replacing conventional product sales with comprehensive solutions. The shift towards PSSs however is problematic given the challenges of integrating products and services. Moreover, views regarding the design of PSSs are diverse and dissimilar. The research discusses the importance of PSSs and analyses the current approaches regarding design methods and design processes in terms of product-service integration. The analysis led to the proposal of a unified, generic design process, built on the Design Science approach where the existing differences in the literature are converged towards a holistic model. The model consists of four stages each including its intricate activities. The stages are built following a structure similar to product design, exposing the key activities to carry out as well as the tools to realize them.