Sigfusson (Icelandic: Þorsteinn Ingi Sigfússon; June 4, 1954 in Vestmannaeyjar, Iceland – July 15, 2019) was an Icelandic physicist prominent in the field of energy research.
He was awarded the Global Energy Prize in 2007, and was the Director of the Innovation Center Iceland at the University of Iceland, where he holds the Icelandic Alloys Chair.