This book examines two topics in the context of product design and enabling technologies: User eXperience (UX) and eXtended Reality (XR). UX regards the ways in which people interact with the environment and with objects and is considered of primary importance in many contexts. When developing new products, UX must be carefully designed and evaluated directly with the users. Prototyping is a well-known, effective, and widely used practice for design evaluation. The book describes how prototyping based on XR technologies, including Virtual, Augmented and Mixed Reality, is a suitable approach for testing ideas and products without fully physically building them. The major benefits, which are well explained and demonstrated in this book, consist in allowing users to experience products, including their appearance, functions, and usability, in a digital context that can be easily modified and customized according to the users' feedback and the context of use. The audience of the book includes graduate students who wish to learn more about prototyping methods and technologies and product and digital application designers who can deepen their knowledge on advanced digital technologies for evaluating the designs of products and experiences.