The Periphery is a fictional location in Isaac Asimov's

Isaac Asimov

Isaac Asimov was an American author and professor of biochemistry at Boston University, best known for his works of science fiction and for his popular science books. Asimov was one of the most prolific writers of all time, having written or edited more than 500 books and an estimated 90,000...

 Foundation Series and refers to the outer rims of the Galactic Empire, including planets such as Anacreon and Santanni. Imperial control is weakest in the periphery, as planet governors there frequently possess their own fleets. Santanni revolts during Forward the Foundation

Forward the Foundation

Forward the Foundation is a novel written by Isaac Asimov. It is the second of two prequels to the Foundation Series. It is written in much the same style as the original novel Foundation, a novel composed of chapters with long intervals in between...

. About 50 years after the First Foundation is established on Terminus, the emperor will grant the periphery autonomy

Autonomy

Autonomy is a concept found in moral, political and bioethical philosophy. Within these contexts, it is the capacity of a rational individual to make an informed, un-coerced decision...

. This effectually removes them completely from Imperial control, making the dissolution of the Empire far more apparent than it had been before.

In the years preceding the fall of Trantor

Trantor

Trantor is a fictional planet in Isaac Asimov's Foundation Series and Empire Series of science fiction novels.Trantor was first described in a short story by Asimov appearing in Early Asimov Volume 1. Later Trantor gained prominence when the 1940s Foundation Series first appeared in print . Asimov...

, the periphery became any area outside the empire as this area became larger the empire became less and less great.

As the empire decreased in size and power the stagnation that would ultimately cause the collapse of the empire increased.