Much of the island's history is provided within The Wicker Man, particularly by the character of Lord Summerisle (Christopher Lee) during a dialogue with the character of Sgt. Howie (Edward Woodward).
According to the film, Summerisle lies off the western coast of Scotland, and once earned a pittance through fishing and sheep farming. In 1868, the (presumably) first Lord Summerisle came to the island, attracted by the volcanic soil and the warm gulf stream surrounding Summerisle, utilising it to grow certain types of fruits and vegetables. In doing so, Lord Summerisle attempted to win over the inhabitants by converting them from Christianity to "the old gods".
When the crops became successful, the inhabitants of Summerisle fully embraced paganism, and the Christian ministers were banished to the mainland. Summerisle continued to be fruitful and prosperous for several years, and the inhabitants continued to worship pagan deities, with particular emphasis on fertility rituals.
The principal events of the film describe the failure of Summerisle's crops, and how the inhabitants lure an outsider from the mainland under false pretences to be sacrificed to their gods in a giant Wicker Man, in the hope that the crops will prosper once again.
No solid layout of the island is given in the film, although notable buildings featured in the film include The Green Man public house, a ruined churchyard, and a small library.
In the 2006 remake, the island is renamed Summersisle, and is changed from a remote island off the west coast of Scotland to a private island situated in the Puget Sound region of Washington state in America.
In the remake, Summersisle is made prosperous by the production of honey, introduced by a local landowner. Like the original film, the inhabitants of Summersisle were convinced to revert to paganism when the island produced high yields of Honey. In the remake, however, the inhabitants also adopted a strict form of matriarchy, and the men of Summersisle were kept solely for breeding or to be sacrificed in giant Wicker Man statues annually to ensure successful harvests of honey each year.
For reasons that go unexplained in the remake, the yield of honey inexplicably drops, and the matriarchs of Summersisle are forced to sacrifice a male from the mainland in the hope of increasing their next yield of honey.
Other fictional locations with pagan connotations appear elsewhere in The Wicker Man Trilogy, all of which are similar to Summerisle in the sense that they are isolated communities whose inhabitants worship some form of non-Christian polytheistic cult.
In the novel (and later film) Cowboys for Christ by Robin Hardy, the role of Summerisle is taken by the fictional village of Tressock, which is located somewhere in the Scottish lowlands. Like The Wicker Man, the inhabitants of Tressock also worship a modern form of Celtic paganism, but have also devised their own unique ritual of "hunting the Laddie", where they hunt down a victim and devour him upon capture.
In the final instalment of the trilogy, Twilight of the Gods, the role of Summerisle is taken by a location in Iceland (as yet unnamed) where the inhabitants practice Norse paganism in the modern day.