The Hollow Man is a 1935 locked room mystery novel by the American writer John Dickson Carr, featuring his recurring investigator Gideon Fell. It contains in chapter 17 the often-reprinted "locked room lecture" in which Dr Fell speaks directly to the reader, setting out the various ways in which murder can be committed in an apparently locked room or otherwise impossible situation.

The "locked-room" or "impossible crime" mystery is a type of crime seen in crime and detective fiction. The crime in question, typically murder, is committed in circumstances under which it appeared impossible for the perpetrator to enter the crime scene, commit the crime, and leave undetected. The crime in question typically involves a situation whereby an intruder could not have left; for example the original literal "locked room": a murder victim found in a windowless room locked from the inside at the time of discovery. Following other conventions of classic detective fiction, the reader is normally presented with the puzzle and all of the clues, and is encouraged to solve the mystery before the solution is revealed in a dramatic climax.