Released in February 1957, Miles Davis’s legendary Birth of The Cool was culled from three days of recordings; two 1949 and one from 1950. As the title infers, these recordings were seminal in the birth of the cool jazz era.

Stephen Thomas Erlewine in Allmusic.com sums it up:

“The Birth of the Cool remains one of the defining, pivotal moments in jazz. This is where the elasticity of bop was married with skillful, big-band arrangements and a relaxed, subdued mood that made it all seem easy, even at its most intricate. After all, there’s a reason why this music was called cool; it has a hip, detached elegance, never getting too hot, even as the rhythms skip and jump. Indeed, the most remarkable thing about these sessions — arranged by Gil Evans and featuring such heavy-hitters as Kai Winding, Gerry Mulligan, Lee Konitz, and Max Roach — is that they sound intimate, as the nonet never pushes too hard, never sounds like the work of nine musicians. Furthermore, the group keeps things short and concise (probably the result of the running time of singles, but the results are the same), which keeps the focus on the tones and tunes. The virtuosity led to relaxing, stylish mood music as the end result — the very thing that came to define West Coast or “cool” jazz — but this music is so inventive, it remains alluring even after its influence has been thoroughly absorbed into the mainstream”

All About Jazz – The Birth of The Cool