"What'll I Do" is a song written by Irving Berlin in 1923.[4] It was introduced by singers Grace Moore and John Steel late in the run of Berlin's third Music Box Revue and was also included in the following year's edition.[5]
"What'll I Do" is one of the few songs by Berlin that is clearly autobiographical. His fiancée, a society beauty named Ellin MacKay, had been sent to Europe by her disapproving father, a very wealthy Long Island magnate, in the hopes that MacKay would forget Berlin. (She did not and eventually they married.) The song was written during McKay's "tour" of Europe. In the lyrics, the singer longs disconsolately for his love, imagining how he can go on without her.