Kai Simons (born 24 May 1938) is a Finnish professor of biochemistry and cell biology and physician living and working in Germany. He introduced the concept of lipid rafts, as well as coined the term trans-Golgi network and proposed its role in protein and lipid sorting. The co-founder and co-organizer of EMBO, ELSO, Simons initiated the foundation of MPI-CBG, where he acted as a director (1998–2006) and a group-leader (until 2012). He is the co-founder and co-owner of Lipotype GmbH.