In order to deliver a foundation for orientation and decisions in the growing field of Mobile Augmented Reality (MAR), this chapter intends to deliver a realistic picture about MAR, where it comes from, where it currently stands, and where it is going. It distinguishes between the variants of MAR, explains their similarities, differences, and different development stages and outlooks. While describing potential application fields and their current limitations, the opportunities and challenges of MAR become obvious, as well as how much work is still to do. The chapter intends to categorize the challenges for MAR, covering also related issues in the mobile hardware, software, and operator industry, and their efforts in standardization and open interfacing. Besides the technology-driven discussion, a strong emphasis will be taken also to the essential aspect of user experience. With ubiquitous MAR, the technology will become more and more secondary, and the user and her individual context moves into the center of attention.