The Great American Songbook refers to a collection of the most important and influential American popular songs and jazz standards from the early 20th century. This repertoire includes works by notable composers and lyricists such as George Gershwin, Irving Berlin, and Cole Porter. These songs often reflect themes of love, loss, and the American experience. Many of the songs in the Great American Songbook have been performed and recorded by various artists, including Frank Sinatra, Ella Fitzgerald, and Billie Holiday. The songs remain popular today, often covered in various musical genres, and continue to influence contemporary music and culture.