Gustaf Allan Pettersson (19 September 1911 – 20 June 1980) was a Swedish composer and violist. He is considered one of the 20th century's most important Swedish composers. In the final decade of his life, his symphonies (typically one-movement works) developed an international following, particularly in Germany and Sweden. Of these, his best known work is Symphony No. 7. His music later found success in the United States. The conductors, Antal Doráti and Sergiu Comissiona, premiered and recorded several of his symphonies. Pettersson's song cycle Barefoot Songs influenced many of his compositions.
Pettersson studied at the Royal Swedish Academy of Music's conservatory. For more than a decade, he was a violist in the Stockholm Concert Society; after retiring he devoted himself exclusively to composition. Later in his life, he suffered from rheumatoid arthritis. Pettersson was awarded the Litteris et Artibus, a Swedish royal medal established in 1853.