Once in a Lifetime is a 1930 play by Moss Hart and George S. Kaufman, the first of eight on which they collaborated in the 1930s.
Hart wrote the original three-act play in 1929. When he shopped it around, producer Sam Harris arranged for Kaufman to work with Hart on several revisions and rewrites.
Hart was a 25-year-old unknown at the time. Kaufman was quite renowned, and it was his name on the marquee which drew in the audiences. At the end of the Broadway opening night, a resounding success which received numerous curtain calls, Kaufman stepped forward and gave a one-line curtain speech, "I would like this audience to know that eighty percent of this play is Moss Hart."