Subliminal advertising is a term used to describe a commercial message or signal embedded within another object. Its intent is to convey a message which will pass below perception's normal limits. In theory, the advertising message is not discernible to the conscious mind, but the subconscious mind is fully aware and inspired to take action by the message. Subliminal methods have been used occasionally in scientific studies, advertising and propaganda, but the effectiveness is debated and is unproven.

The term subliminal advertising was coined by James Vicary a marketing researcher who claimed falsely to have induced people to purchase more food and drink at a New Jersey movie theater during a six-week campaign of flashing the words ''eat popcorn” and ''Drink Coca-Cola” on the screen at 5 second intervals with a 1/3000 of a second duration. Vicary's claims eventually led to the banning of subliminal advertising techniques in the United States, United Kingdom and Australia.

Proponents of the effectiveness of subliminal advertising claim that since the messages are not under conscious control, they would be akin to hypnotic suggestions and therefore MORE effective since they've bypassed the conscious screens put in place by our minds. Critics feel that the effect of subliminal advertising would akin to that of a glimpse of an advertising billboard from the corner of the eye. Controlled experiments have been unable to successfully demonstrate the effectiveness of subliminal advertising.

Another type of subliminal advertising is backmasking, a technique there audio messages are recorded backwards onto a forward tape. The resulting messages sound like nonsense to the conscious mind, but according to fundamentalist Christians, will cause the listeners to participate in the use of drugs and sex. Again, no scientific evidence exists to support this claim.

Many comedic references are obvious subliminal messages, although if most people realize that ''subliminal advertising” is being submitted, it's probably no longer subliminal. Parody examples include Beavis and Butt-head, Family Guy, Clone High and The Simpsons advertising everything from cigarettes, to US Navy recruitment, to the National Rifle Association.

Most examples of assumed subliminal advertising deal with the military, as a response to abysmally low recruitment figures. One Malcolm in the Middle episode has one military type commenting to another ''The subliminal messages must be working.” The other drill sergeant then asks ''What subliminal messages-”

Dean Koontz book Night Chills from 1976 portrays the protagonist and children as vacationing in a small town secretly involved in mind-control and subliminal advertising messages. The only clue to the experiment is the night chills experienced by all of the townspeople involved.

One other area, closely related to subliminal advertising is not the act of inserting one media message into another, but that of showing characters in movies, books and television using various products or taking certain actions without consciously pointing out—''Hey, this hero is using HP computers, therefore you should buy HP computers also-” Many products are donated to movie and television makers in order that the products will appear and be used in the movie or television by the characters.