This study explores Wikipedia as a site for learning. It traces how people learn to become Wikipedia editors through engagement in an editathon, a training event for people who want to become a volunteer editor. The study is original in its emphasis on the various types of knowledge editors acquire as they develop expertise. Determining the knowledge needed to contribute to Wikipedia is significant in terms of understanding Wikipedia as a site for learning. Data was gathered from nine participants who took part in an "editathon" event. The study used a rigorous methodology, combining quantitative social network analysis, documenting the online activity of participants as they created and edited Wikipedia pages, with qualitative interviews about participants' lived experiences during the editathon. Conceptual and procedural knowledge are representative of the foundational knowledge needed to contribute to Wikipedia actively as an editor. However, these knowledge types on their own are not sufficient. Editors also develop socio-cultural and relational forms of knowledge to enable them to operate and problem-solve effectively. The relationship between the physical and the digital is important, since socio-cultural and relational knowledge are developed through active experimentation as the editathon engage with physical objects to create the online wiki pages.