Radio drama (or audio drama, audio play, radio play, radio theatre, or audio theatre) is a dramatised, purely acoustic performance. With no visual component, radio drama depends on dialogue, music and sound effects to help the listener imagine the characters and story: "It is auditory in the physical dimension but equally powerful as a visual force in the psychological dimension." Radio drama includes plays specifically written for radio, docudrama, dramatised works of fiction, as well as plays originally written for the theatre, including musical theatre, and opera.

Radio drama achieved widespread popularity within a decade of its initial development in the 1920s. By the 1940s, it was a leading international popular entertainment. With the advent of television in the 1950s, radio drama began losing its audience. However, it remains popular in much of the world.

Recordings of OTR (old-time radio) survive today in the audio archives of collectors, libraries and museums, as well as several online sites such as the Internet Archive.

By the 21st century, radio drama had a minimal presence on terrestrial radio in the United States, with much American radio drama being restricted to rebroadcasts of programmes from previous decades. However, other nations still have thriving traditions of radio drama. In the United Kingdom, for example, the BBC produces and broadcasts hundreds of new radio plays each year on Radio 3, Radio 4, and Radio 4 Extra. Like the US, Australia's network the ABC has abandoned broadcasting drama but in New Zealand on RNZ, continues to promote and broadcast a variety of drama over its airwaves.

Thanks to advances in digital recording and Internet distribution, radio drama experienced a revival around 2010. Podcasting offered the means of inexpensively creating new radio dramas, in addition to the distribution of vintage programs.

The terms audio drama or audio theatre are sometimes used synonymously with radio drama; however, audio drama or audio theatre may not necessarily be intended specifically for broadcast on radio. Audio drama can also be found on CDs, cassette tapes, podcasts, webcasts, or other digital downloads as well as broadcast radio.

The Roman playwright Seneca has claim as a forerunner of radio drama because "his plays were performed by readers as sound plays, not by actors as stage plays... In this respect Seneca had no significant successors until 20th-century technology made possible the widespread dissemination of sound plays."

Radio drama traces its roots back to the 1880s: "In 1881 French engineer Clement Ader had filed a patent for 'improvements of Telephone Equipment in Theatres'" (Théâtrophone). English-language radio drama seems to have started in the United States. A Rural Line on Education, a brief sketch specifically written for radio, aired on Pittsburgh's KDKA in 1921, according to historian Bill Jaker. Newspaper accounts of the era report on a number of other drama experiments by America's commercial radio stations: KYW broadcast a season of complete operas from Chicago starting in November 1921. In February 1922, entire Broadway musical comedies with the original casts aired from WJZ's Newark studios. Actors Grace George and Herbert Hayes performed an entire play from a San Francisco station in the summer of 1922.