Throughout the twentieth century, folk music has had many definitions and incarnations in the United States and Great Britain. The public has been most aware of its commercial substance and appeal, with the focus on recording artists and their repertoires, but there has been so much more, including a political agenda, folklore theories, grassroots styles, regional promoters, and discussions on what musical forms—blues, hillbilly, gospel, Anglo-Saxon, pop, singer-songwriters, instrumental and/or vocal, international—should be included. These contrasting and conflicting interpretations were particularly evident during the 1950s. This chapter begins by focusing on Alan Lomax (1915–2002), one of the most active folk music collectors, radio promoters, and organizers during the 1940s. Lomax had a major influence on folk music in both the United States and Great Britain, tying together what had come before and what would follow. The chapter then discusses folk festivals and performers; British folk music, musicians, and trans-Atlantic musical connections; and Carl Sandburg's publication of the The American Songbag in 1927.