Dragnet was an American radio series, enacting the cases of a dedicated Los Angeles police detective, Sergeant Joe Friday, and his partners. The show took its name from the police term "dragnet", meaning a system of coordinated measures for apprehending criminals or suspects.

Dragnet is perhaps the most famous and influential police procedural drama in media history. The series gave audience members a feel for the boredom and drudgery, as well as the danger and heroism, of police work. Dragnet earned praise for improving the public opinion of police officers. 

Actor and producer Jack Webb's aims in Dragnet were for realism and unpretentious acting. He achieved both goals, and Dragnet remains a key influence on subsequent police dramas in many media.

The show's cultural impact is such that after seven decades, elements of Dragnet are familiar to those who have never seen or heard the program. The ominous, four-note introduction to the brass and tympani theme music (titled "Danger Ahead"), composed by Walter Schumann, is instantly recognizable.[2] It is derived from Miklós Rózsa's score for the 1946 film version of The Killers.[3] Another Dragnet trademark is the show's opening narration: "Ladies and gentlemen: the story you are about to hear is true. Only the names have been changed to protect the innocent." This underwent minor revisions over time. The "only" and "ladies and gentlemen" were dropped at some point. Variations on this narration have been featured in subsequent crime dramas, and in parodies of the dramas (e.g. "Only the facts have been changed to protect the guilty").

The radio series was the first entry in a Dragnet media franchise encompassing film, television, books and comics.