Bacteria seldom exist in a single cell or free living planktonic state. Instead, bacteria exist in multicellular communities within biofilms. Biofilms are communities of single or multi-species microbes attached to and living on abiotic or biotic surfaces. The biofilm mode growth allows microbes to cope with environmental stress, resist antimicrobials, defend the host immune response, and persist during chronic infections. Biofilms are ubiquitous and occur in natural ecosystems, in additional to industrial, food, and medical settings. The formation of biofilms on medical devices or within human hosts has complicated the treatment of microbial infections. This reference module will focus on some of the new mechanisms employed by microorganisms to form biofilms and persist in the biofilm niche, polymicrobial biofilm interactions that influence disease outcomes, and emerging approaches to investigate biofilms.