Humans and other organisms are under constant threat from deadly invaders—viruses, bacteria and other microbes which infiltrate the body, create dangerous toxins and damage or kill cells. During the course of evolution, organisms developed sophisticated defence mechanisms to deal with these attacks—the immune system as we know it is a product of millions of years of selective pressure. Most functions of the innate immune system, our bodies’ first line of defence against attacks, are shared by all classes of animals and even plants. Today, we know that the immune system is an extremely complex machine, with functional parts distributed across cells and tissues in the entire body. Bruce Beutler, the Director of the Center for Genetics of Host Defense at the UT Southwestern Medical Center, has made some of the key contributions to understanding innate immunity. He discovered an important family of receptors that allow mammals to sense when an infection occurs, triggering a powerful counterattack against the invading cells. His insights have provided the basis for developing new drugs against a range of inflammatory diseases and laid the foundation for further studies on immune defense. For his work, Bruce Beutler was awarded the 2011 Nobel Prize in Physiology or Medicine, which he shared with his colleagues Jules Hoffmann and Ralph M. Steinmann. Today, Beutler’s Lab uses a so-called forward genetic approach to identify genes that are important for innate immunity in mammals and to find out about their specific functions. At Falling Walls, Bruce Beutler explains why the golden age of genetics will allow a better understanding of our own immune system in the struggle against infectious diseases, which still claim more years of human life than any other single cause.