This article describes an assignment that encourages students to create collaboratively designed fantasy worlds. Inspired by the fanfiction genre, a teacher helps students create a world of interlinking stories and develop more detailed, sophisticated writing through in-depth collaboration. The authors present and discuss three salient forms of collaboration: (1) collaboration as maintaining continuity across story lines; (2) collaboration as the borrowing of ideas; and (3) collaboration in consideration of social roles. They argue that collaborative writing in the project helped to establish a social network of student authors who shared an interest in fantasy fiction and came to support each other's writing in productive, yet complex, ways.