You can compare its impact to that which all of Shakesp­e­are's plays and poems have had on English literature, or, closer home, to the imme­a­surable contribution that Rabindranath Tagore's output has had on Bengali culture. The point is that the Great American Songbook is a gi­gantic body of work that serves as the most vital reference point for any ja­zz practitioner.

It's a sort of unoffici­al greatest-hits collection from the re­pertoire of legends from the 1920s to '60s, whose musical innovations ga­ve form and structure to the entire genre. And all later outfits have — or at least should have — studied the standards they framed. You can put it this way — like a devout Catholic is expected to read the Bible, so it is with jazz musicians and the American Songbook.