Thomas Gustafsson (born 25 February 1968), known professionally as Thomas G:son (Swedish pronunciation: [geːʂɔn]) is a Swedish composer and musician.

He is best known for the 117 songs he has written for the national selections of 12 countries for the Eurovision Song Contest: 74 for Sweden, 16 for Spain, six for Norway, five for Denmark and Finland, three for Georgia, two each for Poland, Malta and Cyprus and one each for Latvia, Romania, Belgium, Lithuania, Luxembourg and Armenia. His songs have also reached Eurovision 16 times: four times for Sweden, three times each for Spain and Georgia, twice for Cyprus and once each for Norway, Denmark, Malta and Armenia. In 2012, G:son achieved his first victory as a winning composer at the Eurovision Song Contest with "Euphoria", performed by Loreen. With the same artist in 2023, he won the contest for a second time.

Gustafsson has been a full-time songwriter since 1998. In addition to writing and composing songs in various genres for a living, he is the guitarist of the hard rock band Masquerade.

G:son and Henrik Sethsson's song for the Eurovision Song Contest 2001, "Listen to Your Heartbeat", was accused of plagiarism from Belgium's 1996 entry "Liefde is een kaartspel". The songwriters denied the accusation, but after the Belgian songwriters and the author's organisation SABAM pressed for legal action, a cash settlement was agreed.