"One of Us Must Know (Sooner or Later)" is a song written and recorded by Bob Dylan. It is the fourth track on his 1966 album Blonde on Blonde, and was released as the album's first single that February. The song is an emotional confession of misconnects and apologies from the singer to a woman who has tragically slipped out of his life. As a single, it peaked at #33 in the UK but only reached #119 on Billboard's Bubbling Under charts. According to Jonathan Singer, it was Paul Griffin who played the piano part on "One of Us Must Know (Sooner or Later)".