It is generally acknowledged that biofilms are the dominant lifestyle of bacteria, both in the natural environment as on manmade settings such as industrial and medical devices. This attached form of cell growth consists of slime matrix embedded bacteria of either a single, but mostly of multiple microbial species that form an interdependent structured community, capable of coordinated and collective behavior. Although research on multispecies biofilms is still in its infancy, this review will focus on these complex communities where cooperation and antagonism are keys to increase the fitness of the different species and where intercellular interactions and communication are means to achieve this goal.