Biofilms are groups of attached bacteria, which are both resilient and adaptive. They often show remarkable organization and can communicate, coordinate, and cooperate with each other. The biofilm begins to dispel the notion that bacteria are simply many single cells out for themselves in favor of the idea that they can act as groups of cooperating cells to enhance their individual fitness and increase the efficiency of the biofilm. This is not altruism per se, but rather by exploiting the biofilm, individual fitness is enhanced by the interactions. As with any mutualism or commensalism, this does not rule out selection on individual cells. This notion has transformed microbiology, and forces us to rethink the roles of microbes and how they operate within the earth's many ecosystems.