The workshop on interaction (GTI) is also an interdisciplinary workshop in which the economists at GREQAM interact with sociologists, psychologists, neuroscientists, or physicists. The diversity of points of view may explain that, in accordance with its title, the workshop is always very interactive, but in a friendly atmosphere. The presentations concern one of the two topics of the GTI which are complementary to each other in the analysis of interactions. The first topic is the analysis of multilateral interactions through the use of social networks or multi-agent based models. The second topic concern the analysis of rationality and cognition in bilateral interactions. The workshop meets twice each month on Friday morning. The presentation/debate takes place from 10:30 to 12:00. Members of the working group meet afterwards at the restaurant les Trois Mats for an animated lunch.