So dubbed because these three sessions -- two from early 1949, one from March 1950 -- are where the sound known as cool jazz essentially formed, 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