Not counting jazz standards or traditional folk tunes from before the rock period, which is the most covered song of all time?

'Yesterday' is the most covered song.

It was written by Paul McCartney (credited to Lennon–McCartney), and first released on the album 'Help!' in the United Kingdom in August 1965. McCartney performed it as a solo, alone on the stage or with a string quartet.

It remains popular today with more than 2,200 cover versions, including Joan Baez, Liberace, Frank Sinatra, Elvis Presley, En Vogue, and Boyz II Men.

Other artists who covered this song are quite literally a 'Who's Who' of the modern music industry from Count Basie and Ray Charles to Gladys Knight and the Pips, and Sarah Vaughan.

'Yesterday' was voted the best song of the 20th century in a 1999 BBC Radio 2 poll of music experts and listeners and was also voted the No. 1 pop song of all time by MTV and Rolling Stone magazine the following year. In 1997, the song was inducted into the Grammy Hall of Fame.

In 2012, the BBC reported that Yesterday remained the fourth most successful song of all-time in terms of royalties paid, having amassed a total of £19.5 million ($27 469 845.00 US) in payments. (It is listed as number three on some reference sites.)

'White Christmas', written by Irving Berlin, and made famous by Bing Crosby's version in the movie of the same name, is the undisputed leader having sold more than 100 million copies.