A theory that sf conventions, particularly Worldcon, should encompass the interests of all related fringe fandoms, even though those groups have their own tightly focused conventions, which exclude other interests. Proponents of the Big Tent also tend to object to any definition of fandom or Trufandom that doesn't include all of those groups.
For an example of this philosophy in practice, consider Windycon 40, near Chicago in 2013, which used "The Big Tent" as its theme. The convention featured approximately 50 hours of anime and films; 19 filk concerts; ongoing gaming of numerous types; a track of kids' programming; 11 program items about costuming, plus a masquerade; four program items about art, plus an art show and auction; 10 science programs; six panels about publishing or writing; two panels on political issues; six about TV or films plus four on pop-culture icons spanning print and media (Harry Potter, Superman, etc.); two survey panels discussing types of fandoms; a panel about a proposed Hugo Award; two about fan fiction; five or six miscellaneous items, such as yoga sessions; and, besides readings and autograph sessions, two panels that might have discussed sf books. There was no programming on fanhistory or SF fanzines or discussing the fiction of sf authors, such as the GoH or SFWA Grand Master Frederik Pohl, who had lived outside Chicago since 1984 and died just two months before the con at age 93.