Thelonious Monk wrote "'Round Midnight" as a love song, and then he buried the evidence. He copyrighted the melody on September 24, 1943, under the title "I Need You So," in C minor, with lyrics by a neighborhood friend named Thelma Murray. According to biographer Robin D.G. Kelley, whose book Thelonious Monk: The Life and Times of an American Original remains the definitive account, Monk was at that moment in the early stages of courting Nellie Smith, a student who had spent a year away from New York. Kelley suggests that the Murray lyrics could have easily referred to Monk's longing during Nellie's absence. The melody that would become the most recorded standard composed by a jazz musician began, in other words, as a private letter set to music.

The personal circumstances surrounding the composition were not comfortable ones. Monk had recently lost his position as house pianist at Minton's Playhouse in Harlem, the club where bebop had been incubating through late-night sessions with Dizzy Gillespie, Kenny Clarke, and Charlie Christian. He was playing short-term gigs, living with his mother, and largely unknown outside a tight circle of musicians. The song arrived out of that specific combination: a young man in love, professionally unmoored, writing something inward and slow at a moment when the music around him was accelerating toward bebop's breakneck tempos. The harmonic language of "'Round Midnight," set in E-flat minor with its frequent shifts toward the relative major of G-flat, was already unusual enough to mark it as something apart from the standard repertoire of the day.

The song reached the public not through Monk but through a chain of musical friendship. Bud Powell, Monk's closest peer among bebop pianists, persuaded trumpeter Cootie Williams to record the tune, and Williams did so on August 22, 1944. Williams composed an eight-bar interlude for his arrangement and received a co-composer credit for that contribution. Separately, lyricist Bernie Hanighen added new words; the original "I Need You So" lyrics were dropped, and Hanighen received his own co-credit. Dizzy Gillespie then contributed what became the song's standard introduction, a chromatic phrase he had originally composed for the end of his arrangement of "I Can't Get Started," later adopted as the opening to "'Round Midnight." Monk's own first recording of the tune came on November 21, 1947, for Blue Note Records, a restrained 3:11 version that appeared on "The Genius of Modern Music: Volume 1." By then, the song was already circulating among musicians without him.

The next decisive moment in the song's life came at the Newport Jazz Festival on July 17, 1955, when Miles Davis played "'Round Midnight" as part of an all-star jam session. The personnel that night included Monk himself on piano, along with Zoot Sims on tenor saxophone, Gerry Mulligan on baritone saxophone, Percy Heath on bass, and Connie Kay on drums. Davis, then recently clean from heroin and without a regular working band, put the bell of his horn close to the microphone, a move that festival producer George Wein later recalled as the moment Davis became the star of the festival. George Avakian of Columbia Records was in the audience, and his brother Aram persuaded him to sign Davis to the label. Davis's own response to the reception was typically deflating: "What are they talking about? I just played the way I always play."

Avakian signed Davis to Columbia, and the album that followed, recorded across three sessions on October 26, 1955, June 5, 1956, and September 10, 1956, and released in March 1957 as "'Round About Midnight," was Davis's first record for the label. The quintet he assembled for those sessions has since become one of the most studied small groups in jazz history: John Coltrane on tenor saxophone, Red Garland on piano, Paul Chambers on bass, and Philly Joe Jones on drums. The title track itself was recorded on September 10, 1956, at Columbia's 30th Street Studio in Manhattan, produced by Avakian. On the studio version, Davis played through a Harmon mute held close to the microphone, a sound warm and interior, almost conversational. Whereas the Prestige sessions from the same period were largely first-take, no-rehearsal affairs, the Columbia dates involved multiple takes of carefully selected material, with the final release spliced from the better portions of two or more runs. Ralph J. Gleason, reviewing the album in the May 16, 1957, issue of DownBeat, awarded it five stars, calling it "modern jazz conceived and executed in the very best style."

What the story of "'Round Midnight" makes visible is how much of bebop's emotional interior was built from private material, longing, displacement, the specific grief of a particular person's absence, that the music then transformed into something structural and impersonal enough to survive any performance. Monk dropped the lyrics and let the harmony carry the feeling. A version recorded by Monk's quintet was added to the Grammy Hall of Fame in 1993. The love letter became a standard because Monk trusted the chords to say what the words had already said, and every musician who has played it since has been, in some sense, reading someone else's mail.