Over recent years Web 2.0 has brought information into the hands of the public, and we are increasingly seeing non-professionals doing sophisticated information tasks not merely for work, research or personal interest, but also for leisure-and even pleasure. This paper looks at an online fanfiction repository, Archive of Our Own (AO3), and investigates the ways that media fans have co-opted new technologies to build a 'curated folksonomy' (Bullard 2014), in order to organise the fanworks (fan-created creative works) uploaded by fans to the website. Run by volunteers, the site is a fascinating example of how passion, and even obsession, can bring amateur knowledge workers together collaboratively with users to build an intricate 'democratic indexing' system (Hidderley and Rafferty 1997; Rafferty and Hidderley 2007). Through methods of tag analysis and interviews, the paper explores how Archive of Our Own's curated folksonomy allows fans to make full and creative use of their own original, freeform tags, while also building a highly granular and sophisticated taxonomy which, though highly labour-intensive to maintain, serves the community by maintaining a high degree of accuracy while also preserving the folksonomic properties of freeform tagging. As well as building a functioning taxonomy, through standardising its nomenclature, and facilitating the discoverability of AO3's collections to its users, these amateur knowledge workers see their domain expertise and knowledge organisation labour as a type of fanwork that 'gives back to the community', in lieu of other creative works such as fanfiction and fanart.