"I Don't Know Why (I Just Do)" is a 1931 popular song. The music was written by Fred E. Ahlert, the lyrics by Roy Turk. The song was published in 1931. It had three periods of great popularity: in 1931, right after its publication; in 1946; and in 1961 into 1962. In 1931, the biggest-selling version was either by Russ Columbo or by Wayne King; both versions and recordings by Bennie Krueger's orchestra (with a vocal by Smith Ballew) and by Kate Smith all had significant popularity.