Woody Guthrie was the most important American folk music artist of the first half of the 20th century, in part because he turned out to be such a major influence on the popular music of the second half of the 20th century, a period when he himself was largely inactive. His greatest significance lies in his songwriting, beginning with the standard "This Land Is Your Land" and including such much-covered works as "Deportee," "Do Re Mi," "Grand Coulee Dam," "Hard, Ain't It Hard," "Hard Travelin'," "I Ain't Got No Home," "1913 Massacre," "Oklahoma Hills," "Pastures of Plenty," "Ph...