This book covers the topic of On-orbit repair and servicing of spacecraft. Putting a communications satellite in synchronous orbit will set you back 100's of millions of dollars. Once on orbit, you hope it survived the launch environment, and operates correctly. And, you further hope it works at least for its design lifetime, and as long as possible. This approach, based on good engineering design practices, lessons learned, and hope, it the equivalent of buying a new S-class Mercedes with a sealed gas tank, and driving it until it stops. Then buying a new one.We will discuss the history and the technology of on-orbit servicing, and the projects currently being conducted. We'll take a look at ambitious planned projects, and the enabling technologies that will make them a success. We'll speculate what this means to missions to other planets in our solar system, and the challenges to manned expeditions to follow the robotic ones. By developing a Orbital Servicing Infrastructure, we could extend the life of very expensive resources, and clean up some of the orbital clutter that is endangering current and future space assets. IOn addition, we can derive a stong business case for on-orbit repair.