Archival and other historical evidence, including digitized issues of The Radio Times and files from the British Broadcasting Corporation’s Written Archives Centre, reveal the pivotal importance that natural history played in the BBC’s programming during the 1920s and 1930s. Beyond merely replicating the forms and styles that could be found across other forms of mass media, natural history broadcasts demonstrated to the British public what radio technology was capable of. At the same time, radio was not isolated from the media landscape of the period, and natural history broadcasts made full use of visual accompaniments such as magazines and pamphlets. Examining a variety of different broadcasts, this paper focuses on how expertise was fashioned behind the microphone, on “stunts” such as broadcasting the live sounds of animals, on audience participation, and on broadcasts aimed at young audiences. Broadcast lessons for schools, which are generally overlooked by historians, offer a rich opportunity for examining how natural history radio developed over the years. Children’s hour characters like the “Zoo Man” modelled an intimate, direct way of engaging with young audiences. Moreover, experiments in field ecology involving listeners in the collection of data showed that radio could act as a two-way medium. These broadcasts helped to shape the modern phenomenon of the nature documentary that would take off after 1945. While the origins of this phenomenon are usually traced either to the establishment of the BBC’s Natural History Unit in 1957, or in some cases to early nature films, there is a strong case for considering the BBC’s interwar broadcasts (1922–1939) as part of this trajectory.