What's My Line? was a weekly panel game show originally produced by Mark Goodson and Bill Todman for CBS television. The series, which was usually broadcast live, debuted on Thursday, February 2, 1950 at 8:00 p.m. ET and aired on alternating weeks. On Wednesday, April 12, 1950, the broadcast was moved to alternate Wednesday evenings at 9:00 p.m. ET. On Sunday, October 1, 1950, CBS moved the show to weekly on Sundays at 10:30 p.m. ET, where it would remain until the end of its network run.

The original series ran for eighteen seasons, ending its run on September 3, 1967. It is the longest-running game show in the history of prime time network television, and the sixth longest-running game show overall (behind It's Academic, The Price Is Right, Wheel of Fortune, Hollywood Squares, Jeopardy! and Concentration).

From 1968 to 1975, a daily (Monday to Friday) version was produced by Goodson-Todman Productions for syndication, and was distributed by CBS Enterprises, which was renamed Viacom Enterprises in 1971. During its run, What's My Line? won three Emmy Awards for "Best Quiz or Audience Participation Show," in 1952, 1953 and 1958.

Contestants with unusual occupations were interviewed by the panelists. Only questions that could be answered with a "yes" or "no" were allowed. At the conclusion of the questioning, the panelists attempted to guess the contestants occupation. There was also a "mystery guest", usually a famous person; the panelists had to wear masks when questioning this person and the guest usually disguised his/her voice. Written by J.E. McKillop

The original version of the all-time classic panel game, which produced 876 shows between 1950 and 1967. Four celebrity panelists tried to determine, through questioning, the occupation of the contestant. The panelists could only ask questions that could be answered yes, no or similar answer, with the contestant winning $5 per "no" answer. The game ended either upon 10 "no" answers, a panelist correctly guessing the player's secret or at the discretion of the moderator. Usually but not always, the last segment saw the now-blindfolded panelists attempt to determine the identity of a mystery guest, who always disguised his voice in an attempt to avoid being identified. For many years, the regular panelists of Arlene Francis, Dorothy Kilgallen and Bennett Cerf were welcome visitors in many homes during the 10:30 p.m. EST Sunday "What's My Line?" airing; a fourth seat was used for guest panelists, though that seat, too, was filled by regulars including Steve Allen (who left for other TV projects) and Fred Allen (who died in 1956) through the years. After Kilgallen's 1965 death, her seat, too, was filled by a guest panelist. Host Daly was reserved as the emergency mystery guest, but was never needed; he would serve as the scheduled mystery guest for the show's final CBS airing in September 1967. "What's My Line?" was updated for syndication in 1968, with new host Wally Bruner (later Larry Blyden). Longtime Arlene Francis returned for the new version, along with newcomer Soupy Sales; Bennett Cerf also made frequent visits until his 1971 death. A 1975 special, "'What's My Line?' at 25," recalled some of the best moments from the CBS series. "What's My Line?" remains one of TV's most fondly remembered game shows and currently airs as part of Game Show Network's Black and White Overnight programming block. At one point, CBS and Pearson TV planned a new version of "What's My Line," with a new celebrity panel but with the same rules; however, those plans never came to fruition. Written by Brian Rathjen

In this five-day-a-week update of the 1950-1967 game show, four celebrity panelists tried to determine through questioning the occupation and/or related secret of the contestant. The panelists could only ask questions that could be answered yes, no or similar answer, with the contestant winning $5 per "no" answer (at least in the early years, this method of scoring was dropped after Larry Blyden became moderator). The game ended either upon 10 "no" answers, a panelist correctly guessing the player's secret or at the discretion of the moderator. The contestant often demonstrated his skill or product, though on many occasions the panelists were invited to try out the skill. During the final segment of the day, the panelists (now blindfolded) tried to determine the identity of a mystery guest who, as before, disguised his voice in an attempt to avoid being identified. On occassion, a new segment, "Who's Who?" required the panelists to correctly match occupations with four audience members who were invited onstage; the contestant team won $25 per incorrect match up to a maximum of $100. Written by Brian Rathjen