This article revisits the relationship between the Communist Party and the BBC in the interwar period, arguing that Communism was a spectre that haunted the early BBC, inhabiting the vision that shaped its formation. More particularly, it argues that Communists proved an influential if uneven presence on BBC radio in the 1930s. It is about Communists on the wireless in both senses: it recovers Communist presence on the airwaves across BBC departments and regions; it also restores to view a body of pre-war Marxist analysis of the technology and cultural form or radio, of the institution of the BBC, and of the possibilities for oppositional interventions. Drawing upon a range of sources from radio listings, Communist Party publications, BBC records, and the declassified MI5 files of broadcasting Communists, it situates the work of Communists on the radio - and the ensuing patterns of BBC blacklisting and censorship - in relation to the histories of both institutions through a tumultuous period.