This book examines the "definition/delimitation question" with special regard to the passage of spacecraft through foreign airspace in order to reach orbit, as well as for returning to Earth. This is particularly important for space transportation systems like the US Space Shuttle or the Soviet Buran, which were used in the past. New systems are already planned in the US, Europe, and China. However, they will all encounter the same "passage problems" as their two predecessors, according to the present and foreseeable state of space technology. The book starts with a presentation of the relevant technical basics, which are then followed by legal considerations, taking into account the extremely sensitive space environment where civilian, commercial, and governmental (including military) activities are conducted by fundamentally different actors with diverging interests and philosophies. In this context, State practices with respect to passage rights, as well as agreements with respect to abort and emergency landing sites on foreign territory, are also discussed. As an annex, a comprehensive selection of relevant documents is reprinted. (Series: Essential Air and Space Law - Vol. 12)