This doctoral thesis is intended to promote the introduction of integrated engineering of products and services. The main contribution is a new development methodology for Product-Service Systems (PSS) and especially for Industrial Product-Service Systems (IPS2). PSS are systems integrating products and services as equivalent solution elements in order to maintain innovative business models providing added value for customers. The PSS development methodology includes a specific system model, a generic PSS development process model and PSS design methods to support early development phases, i.e. the PSS planning and requirements engineering.