Fritiof Stig Sjöstrand (5 November 1912 – 6 April 2011) was a Swedish physician and histologist born in Stockholm. He started his medical education at Karolinska Institutet in 1933, where he received his Ph.D. Karolinska Institutet in 1944. Sjöstrand worked as an assistant at the department of pharmacology, where he first had used polarization microscopy, he first heard about the new method of electron microscopy in 1938, within which he would become a pioneer. Manne Siegbahn at the Nobel Institute for Physics had planned to build an electron microscope in Sweden, and Sjöstrand got involved in the project to explore its use in medical research. The main challenge was to produce sufficiently thin samples, and Sjöstrand's method for producing ultrathin tissue samples was published in Nature in 1943. However, it seemed that research based on electron microscopy would be too time-consuming for a Ph.D. thesis, so his 1944 thesis was based on fluorescence spectroscopy. In 1947-1948, he received a scholarship to further study electron microscopy at Massachusetts Institute of Technology's Department of Biology. Back in Sweden, he received funding to build up an electron microscopy research laboratory. In 1959, Sjöstrand was both offered a position as professor of histology at Karolinska Institutet, and as professor at University of California, Los Angeles (UCLA). He chose UCLA, because conditions for research and funding were better there.