This thesis aims to widen a Methodology, based on the principles and techniques of Lean Thinking, which allows Companies to improve their Product Development processes into a methodology that also improves the service development process. It tries to give an answer to the Companies need to review and optimize their Product-Service development processes affected by constantly changing markets and increasingly complex customers. The Methodology proposal is a result of the work of previous colleagues that was originated from the Lean Thinking techniques and their application in Product Development field. Afterwards, it has been adapted and tested by carrying on some “on the field” experiences with business subjects who have provided key knowledge to its refinement. The Methodology seeks at continuous improvement of the Product-Service Development processes which are consonant with the context in which Companies operate. This means that when a corrective action is carried out it cannot be exclude from future analysis because maybe in those future analysis the change is a waste. This also fits with the Lean perspective that put the constant research for perfection as one of its pillar. For the same reason it is a recursive Methodology compound by five steps, that go from the systematic identification of waste in PSD process, to their removal, until the introduction of targeted corrective actions. Those steps are: 1. Waste Identification & Evaluation. The starting point to develop this phase is an existing list of waste likely to be found in NPSD processes and a Priority Index (PI) to evaluate them. This phase is the one widened so as to include and include the service into the product development analysis. 2. Waste Prioritization. On the basis of the PI, in this phase wastes are put in a priority order and the first to be removed are chosen. Beside this, in association to them also potential detection ways and corrective actions are defined. 3. Sub process identification. It consists in the determination of the sub process affected by the main wastes and so to be improved. 4. Sub process analysis. This phase deals with the sub process analysis to find the critical and eliminate them. Also in this phase several alternative methods have been proposed, with a deepening on Value Stream Analysis and Map. 5. Corrective Actions. In this phase, the correctives actions to be implemented are chosen according to the effort required and the effect that they produce, PICK matrix as a tool is suggested. 2 To test the previous steps listed and also to acquire some feedback about the rightness of the methodology, two cases were conducted. On the one hand, the 5 steps were applied in the car sharing company Car2go which is a very clear example of a product-service. On the other hand, the Politecnico di Milano involvement in Manutelligence consortium gave the opportunity to be in touch with Fundació CIM (based in Barcelona) which manages several Ateneus of Digital Fabrication. These ADFs are places where everyone can go with an idea and transform it into a prototype. Thanks to this collaboration, it was provided another case study with different level of servitization (compared to de Car2go one) on which to perform the first full application of the Methodology. As a result, these activities have highlighted the forces of the Methodology that are its intuitiveness, short implementation time and easy to implement by people without experience, after a brief introduction to Lean Thinking and its techniques. At the same time, several limits have been found and accepted as starting points for future researches and insights. The thesis is structured in the following Chapters:  Chapter 1, Product-Service Systems: This is the opening Chapter, it provides an overview of the context in which the work has been developed, focusing in particular on the current importance of Product-Service Systems. In addition, it explains the objectives and the structure of the thesis are stated.  Chapter 2, Tools and Methodologies for LPSD process: State of the Art: This Chapter is a deep analysis of literature on Lean, by exploring its principles and technique and it shows the state of the art as regards to their application in Product-Service Development context.  Chapter 3, The proposed methodology: In this Chapter is shown the initial methodology in which is based the new one and a guide to its implementation is provided. Then, the additions to it are explained and the process to get to them is detailed.  Chapter 4, Business Case Application: It exposes the business cases of Car2go and ADF giving complete examples of Methodology implementation.  Chapter 5, Conclusions: This is the final Chapter where a summary of the methodology analysis is given and suggests future researches and investigations.