Sayshell is a planet in Foundation's Edge by Isaac Asimov. At the time of the novel, it was capital of the 86 worlds in the Sayshell Union. During Imperial times, it had been capital of the Sayshell Sector. It was 10,000 parsecs (32,600 lightyears) from Terminus.

Throughout much of the pre-Imperial era, Sayshellians were dominated by religious conservatives, who believed that Sayshell was the first planet settled by people from Earth, and from Sayshell the rest of the Galaxy was settled. Due to the pervasiveness of this belief, Sayshell was strongly nationalistic even during the years of the Empire. In 305 F.E. it signed a declaration of neutrality and friendship with the Mule. By 498 F.E., the Sayshell Union continued its nationalism. Most Sayshellians resented the strong control of the Foundation (though not openly).

During the Galactic Era, the Sayshellian Viceroy launched an expedition to conquer Gaia. After Sayshell rebelled from Imperial control, it launched another expedition, roughly a century after the first one. This also failed.

One Sayshellian constellation is known, called the Five Sisters, said to represent the five aspects of love. A dim star in the centre represented unrequited love, and was said to have faded. This was the star around which Gaia orbited. Because of its position, Gaia came to be known by a number of aphorisms, including 'little brother of the Five Sisters', 'the Pentagon's centre', and '0 pentagon'.

The inhabited planet is Sayshell IV; its chief city is Sayshell city, the capital.