The social activities and organization of bacteria are crucial to their ecological success. But it is only in recent years that we have begun to study these secret societies. Most surfaces on this planet teem with microbial life, creating ecosystems of diverse organisms that flourish in slimy beds of their own making. The plaque encrusting our teeth, the slippery coating on river stones, the gunge clogging up water pipes or infected wounds: these are just a few examples of the microbial 'biofilms' that form anywhere there is a surface with a little moisture and some nutrients.