Friedemann Schulz von Thun is a German psychologist and expert for interpersonal communication and intrapersonal communication. Schulz von Thun worked as a professor of psychology at the University of Hamburg until his retirement on 30 Sep. 2009. Among his various publications is a three-part book series titled Miteinander Reden ("Talking With Each Other") which has become a standard textbook series in Germany and is widely taught in schools, universities, and vocational skills training. He developed a number of comprehensive theoretical models to help people understand the determinants and processes of inter-personal exchange and their embeddedness in the individual inner states and the outward situation. For that purpose, he invented the four sides model.