Rhythm and Blues was not generally recognised as a distinct musical genre until the years following the end of World War II. These 4CD sets centred on 1940-1944 attempt to pinpoint records typical of the various strands of music which coalesced into what can now be seen as a historically definable form of black popular music, commonly abbreviated to R&B. Previously, the American record industry had marketed blues, jazz, jug band, hokum, sacred and novelty music under the catch-all phrase, race music. After the war, an increasing sensitivity to racism generated the need for a new term which emerged from a renaming of Billboard's Best Selling Retail Rhythm And Blues Records. A new audience for blues was opening up amongst white record buyers and concertgoers, due to the enormous popularity of boogie-woogie, which was first recorded in jazz band format in 1936 and was by 1940 at the height of its popularity. This period saw the end of mass recording of discs in the downhome and urban blues styles and these artists were largely absent from the studios until the late 1940s, when the electric guitar became the instrument of choice for blues singers. America s entry into the Second World War had the effect of limiting the supply of shellac, which was essential to the manufacture of records. As a result, the number of discs released was severely curtailed and many were only issued to jukebox owners. The unforeseen result of this recording hiatus was a breathing space for the development of two new forms of music that broke through after the end of the war: Rhythm and Blues and bebop.