The Jacques Monod conference "Insect Immunity in Action: From Fundamental Mechanisms of Host Defense to Resistance Against Infections in Nature," organized by Ulrich Theopold (Stockholm University, Sweden) and Dominique Ferrandon (CNRS, France), was held in May 2009 in Aussois, France. Here, we review key topics and concepts that were presented and highlight emerging trends in the field of insect immunity.