'Participatory culture' is a concept which gives consumers an active role in the production and design of commodities and content. Companies embracing user co-creation practices enable consumers to become contributors and producers of the products and services they care about. However, the approach taken by entertainment industries, IP owners of the most popular and beloved fictional worlds, generally gives little room for user involvement in the development and production of their entertainment franchises. These franchised worlds commonly become transmedia giants through commissioning works to professionals and subsidiary and/or external companies and by issuing brand licenses to third party organisations. Collaboration among these elites makes possible for franchise owners to control the intellectual property while increasing the revenue. Even though user participation might be encouraged to a certain degree, this call generally responds to a marketing strategy to strengthen the sales and the bonds between the company and the fan community. User narrative contributions to these imaginary worlds are merely treated as fan-fiction and are, in many cases, liable to be exploited by their franchise owners. Located at the other extreme of the user-agency spectrum, participatory worlds are shared and interactive worlds generally supported by independent ventures which allow and encourage audiences to contribute meaningfully and canonically to their development and expansion. Contributions may be shared in a variety of media modes, genres and formats and through different channels for collaboration and circulation. Similarly, participatory worlds often are spaces where audiences can challenge and divert the original authors' plans about the progress of the storylines and, even, the whole imaginary world. The nature of these spaces commonly goes beyond the ‘traditional’ notions of authorship, audience and participation advocated by the entertainment industries and the mainstream system of textual production. This paper attempts to give a more accurate definition of participatory worlds and demonstrate how audiences can contribute meaningfully to expand them.