Siv Gun Elisabeth Andersson (born 1959) is a Swedish evolutionary biologist, professor of molecular evolution at Uppsala University. She is member of both the Royal Swedish Academy of Sciences and of Engineering. She is also Head of basic research at the Knut and Alice Wallenberg Foundation and has been co-director of the Swedish national center for large-scale research Science for Life Laboratory between 2017 and 2021. Her research focuses on the evolution of bacteria, mainly on intracellular parasites.