The Pennsic War is the largest annual event of the Society for Creative Anachronism. It is held at Cooper's Lake Campground near Butler, PA during the second and third weeks of August. Since 1994, annual attendance has been steady at approximately 10,000; people attend regularly from as far away as Japan, Finland, and Australia.

First held in 1972, the Pennsic War is fought between the East Kingdom and Middle Kingdom, who alternate taking primary responsibility for the event. The event features five or six mass battles, with between 3000 and 4000 fighters participating. There are also a dozen classroom tents which are busy for most of the event, hundreds of parties and informal singing circles, European Renaissance and Middle Eastern dancing from mid-afternoon until dawn, and well over 300 merchants.