The Periphery is a name collectively given to the inhabited planets that fall outside the main zone of influence of Trantor. Asimov states that there are twenty-five million inhabited planets in the Galaxy. It is not clear exactly how many of them fall in the Periphery, but it must be a majority. They are far apart, and far from Trantor, which makes them vulnerable to revolts initiated by local politicians. It is important to note that life in the Periphery can be quite different from life in Trantor and the planets immediately surrounding it. Some worlds on the Periphery are quite "primitive" by Trantor standards.