In this book, we develop strategic and operational level decision making tools to help manage product upgrades in closed loop supply chains under limited availability of upgrade resources. The models developed in this research are mainly applicable to products that are modular, repairable and expensive. This research was directly motivated by a research project done for the United States Coast Guard (USCG) to help them plan an aircraft upgrade from an older to newer version. The upgrade also involved upgrading an aircraft component (gearbox) in order to achieve higher operational efficiency. Apart from developing the planning tools, we also study how the decisions made by these planning tools vary under different levels of operational flexibility.