Until 1997, "What's My Line?" stood as the longest-lived game show in American television history. Its 25-year run on CBS and syndication was attributed to its very simple concept: Guess the contestant's occupation.

The show had enjoyed a 17-year run on CBS, from 1950 through 1967, before beginning a five-day-a-week syndicated run in 1968. The CBS format and its hallmarks were carried over to the syndicated version.

A contestant introduced him/herself, and the host gave a brief clue as to the contestant's occupation or other secret (e.g., "He's involved in a service"). It was up to the four-member celebrity panel to identify the occupation. That was done through asking questions — e.g., "Is it bigger than a breadbox" — that could be answered with a yes, no or similar response. A celebrity could continue his/her questioning until getting a negative response, at which point the next celebrity in line took over. Each "no" response paid $5, at least early in the run. The game ended upon a successful guess, 10 "no" replies or at the host's discretion.

Unlike the CBS version, the contestant's secret was illustrated with such things as film clips and live demonstrations. The demonstrations often took up a good chunk of the show, and made for some of the run's best-remembered moments.

Two "guess the occupation" games were played. The final segment of the day was the "Mystery Guest" segment. As in the CBS version, each celebrity panelist was blindfolded, and the mystery guest — always a well-known celebrity — would disguise his/her voice in such a way as to fool the panel. An incorrect guess as to the celebrity's identity immediately disqualified him/her.

The "guess the occupation" and "Mystery Guest" segments were frequently augmented by a new feature called "Who's Who?" There, four studio audience members were invited on stage, and a board was presented with each one's occupation. One at a time, each celebirty tried to match up the occupations with the correct person; the contestant team was paid $20 for each wrong guess and $100 for a complete stumper.

The first syndicated host was former television news reporter Wally Bruner; he was succeded in 1972 by Larry Blyden. Arlene Francis, a panelist with the CBS show since its second broadcast in February 1950, was back as a regular; joining her as a regular was comedian Soupy Sales. Longtime panelist Bennett Cerf was a semi-regular (until his death in 1971); other frequent guests included Alan Alda, Joanna Barnes, Bert Convy, Gene Rayburn, Nipsey Russell and Gene Shalat. Johnny Olson was the orignal announcer; he left in 1972 and was replaced by Chet Gould.

The 1968-1975 syndicated version represents the last American televised version of the series. Several revivals had been planned starting in the early 1980s, but none ever made it to air; the latest pilot featured host Harry Anderson ("Night Court") and announcer Burton Richardson. Live stage versions, based on the classic format, have been running since 2004.

By the way, "What's My Line's" 25-year longevity run was surpassed by the current version of "The Price is Right." An ABC late-night special, "What's My Line at 25" aired in 1975 and starred Francis, producer Mark Goodson and original CBS host John Daly.