The current media ecosystem offers enormous participatory possibilities to media audiences that, in this way, have the opportunity to engage in the co-creation of media discourse in ways unknown during the 20th century. Following the marketing 2.0 theories, the creation of attractive user experiences is considered as one of the aspects that the media increasingly take into consideration in order to get profitable content. The aim of this research is to detect the factors that influence engagement in podcasting, a digital and interactive medium that, due to its transmedia and mostly amateur nature, develops dynamics of permanent connection between media creators and listeners. By conducting a total of 17 in-depth semi-structured interviews with pioneers of the medium, podcasters and listeners, a total of 13 factors that determine user engagement were identified. These factors are integrated in three groups: medium-centered (technology, asynchrony, topics, genres and formats, and podcast subcommunity’s size), user-centered (participatory culture, consumption situation and number of subscriptions, knowledge on the topic and about the podcast subcommunity, their own relevance in the podcastphere, and the perceived relevance about their participation), and podcaster-centered (skills, attitude and tone). These factors maintain relations of interoperability that build a grammar of engagement of the medium. This study provides some clues that can be exploited by commercial media that are opting for podcasting in order to build innovative experiences of interaction with their users with the purpose of increasing their audiences.