At 2:30 on March 2, 1959, the 32-year-old trumpet player and bandleader Miles Davis took six sidemen into a New York City studio, where they spent the afternoon and early evening recording three songs.

On April 22, the same cohort, minus one of the two piano players who worked on the first date, returned to the same studio and recorded two more songs. As far as the musicians were concerned, that was the end of the story. For the rest of the world, it was just beginning.

Four months later, the five selections were released on the album Kind of Blue. The record became an immediate success, embraced by jazz fans, critics and musicians. Two songs on the album, “So What" and “All Blues," quickly became staples in the jazz repertoire. “So What" even became a favorite of college and high-school marching bands. Meanwhile, the record kept selling, and selling and selling. Today, 50 years after it was released, Kind of Blue remains the bestselling jazz album of all time. More than 4 million copies have been sold, and the album still sells an average of 5,000 copies a week. If you have a jazz album on your shelf, odds are it's Kind of Blue.

Why this album?

Out of the thousands of jazz albums ever recorded, why does Kind of Blue maintain its hold on our imaginations more than any other? The simplest response is to say, because it's beautiful. You won't find many recordings that boast more thoughtful compositions or performances of any higher caliber than the solos and ensemble work of Davis, John Coltrane, Cannonball Adderley, Bill Evans, Wynton Kelly, Paul Chambers and Jimmy Cobb.

The music has no weak spots. Or perhaps it's the unthreatening nature of the music: five medium-tempo selections, all played at the level of human conversation. There's nothing in these songs that would scare anyone. On the other hand, there are none of the signposts or road maps that make jazz accessible to listenersno standards that you can hum, no vocals. And yet, even when you hear this album for the first time, it's like meeting an old friend. It sounds familiar somehow. Even today, at 50, Kind of Blue sounds, as Quincy Jones puts it, “like it was made yesterday."

Old yet new, strange but familiarhow can music possess such contrary qualities and still sound coherent? In the case of this album, it's because the music was designed that way. It coheres because it was conceived as a whole. Each cut contributes to the whole (in this sense, it might better be titled “Kinds of Blue"). One of the most important elements built in from the start was an open-ended sense of discovery and exploration. The men who performed on the two recording dates knew almost nothing about the music they would play before they entered the studio. As Bill Evans, the principal piano player on both recording dates, wrote in his liner notes for the album, “Miles conceived these settings only hours before the recording dates and arrived with sketches which indicated to the group what was to be played. Therefore, you will hear something close to pure spontaneity in these performances."

Davis's sketches, at least a couple of them collaborations with Evans, are more like themes or motifs than fleshed-out songs. But this was the beauty of the challenge: the score demanded a lot of the players that day, because it left so much space for a soloist to fill. The musicians responded by giving the space between the notes the same weight they gave what is played. Their silences really are golden. Listening to these performances is to be reminded of Robert Frost's dictum about the making of a great poem: “No surprise in the writer, no surprise in the reader."

You don't have to know any music theory to appreciate this music, but understanding the context in which it was created does help clarify what Davis was trying to do. Since the '40s, jazz had been dominated by bebop and then hard bop, music characterized by frenetic tempos and chord changes stacked upon chord changes. It required deep musical sophistication to play that style, but while Davis had the chops for bophad indeed been one of its prime movershe had lost his enthusiasm.

“I think a movement in jazz is beginning away from the conventional string of chords," he told an interviewer six months before the recording of this album. “There will be fewer chords but infinite possibilities as to what to do with them. Classical composerssome of themhave been writing this way for years, but jazz musicians seldom have." So he deliberately went another way with Kind of Blue, supplying the barest hint of a song in each case, giving his musicians the scale or scales upon which to improvise and then turning them loose to create their own melodies and variations. It was a return to and an exaltation of lyricism.

Kind of Blue draws on the two essential tributaries of jazzimprovisation and the bluesto create music full of space and possibility, certainly music that appealed to players and listeners alike.