Steen Rasmussen (born 7 July 1955) is a Danish physicist mainly working in the areas of artificial life and complex systems. He is currently a professor in physics and a center director at University of Southern Denmark as well as an external research professor at the Santa Fe Institute. His formal training was at the Technical University of Denmark (1985 PhD in physics of complex systems) and University of Copenhagen (philosophy). He spent 20 years as a researcher at Los Alamos National Laboratory (1988-2007) the last five years as a leader of the Self-Organized Systems team. He has been part of the Santa Fe Institute since 1988.