The character of Henry Orient was inspired by real-life concert pianist Oscar Levant. Nora Johnson, who wrote the novel on which the movie was based (and co-wrote the screenplay with her father, Nunnally Johnson), said that she and a friend had a crush on Levant when they were schoolgirls.
The phone Henry Orient (Peter Sellers) used in his bedroom is called a Ericofon, made by L.M. Ericsson of Sweden. This is one of the very few foreign phones allowed in the U.S. at the time of filming by the then telephone company, Bell Telephone, which held a monopoly on telephone service and telephone equipment in the US. Bell Telephone felt so threatened by the unique European design (and possible mass intrusion into "their" telephone network) that they designed the "Trimline" phone as a countermeasure.
Elmer Bernstein was a top composer of dramatic music with such hits as The Magnificent Seven (1960) and To Kill a Mockingbird (1962), the latter often ranked among the best scores in film history. This was his first collaboration with George Roy Hill in this comedy, a genre he would rule in later years with Stripes (1981), Ghostbusters (1984), Animal House (1978), Trading Places (1983), and Thoroughly Modern Millie (1967), which brought him his only Oscar win over his 14 Academy Award nominations.
Included among the American Film Institute's 2000 list of the 500 movies nominated for the Top 100 Funniest American Movies.