Even after carefully studying the Product Owner role from many angles, this book taught me a lot about this role. For example, among many other things, Roman Pichler did a great job describing many relationships, and of course, focused on the many relationships that the Product Owner has, both with the development teams, the rest of the organization (management, departments, etc.) and, the customers. To accomplish this, Roman describes the organizational contexts so that a Product Owner can establish the right relationships and address the critical aspects of the role effectively. If one wants to extend critical PO skills beyond this book, consider Jeff Patton’s User Story Mapping and Eric Reis’s The Lean Startup. Those will provide an amazingly great core set of knowledge. To extend to larger projects with a true scrum framework, consider the coming book by Craig Larman and Bas Vodde, Large-Scale Scrum: More with LeSS (if you want a large number of details, consider their book Scaling Lean and Agile Development and it’s companion. These are two of the best books I've seen on scrum and in particular, scaling effectively).