Bacteria within the oral cavity live primarily as complex, polymicrobial biofilms. Dental biofilms are necessary etiological factors for dental caries and periodontal diseases but have also been implicated in diseases outside the oral cavity. Biofilm is the preferred lifestyle for bacteria, and biofilms are found on almost any surface in nature. Bacteria growing within a biofilm exhibit an altered phenotype. Substantial changes in gene expression occur when bacteria are in close proximity or physical contact with one another or with the host. This may facilitate nutritional co‐operation, cell–cell signaling, and gene transfer, including transfer of antibiotic‐resistance genes, thus rendering biofilm bacteria with properties other than those found in free‐floating, planktonic bacteria. We will discuss biofilm properties and possible consequences for future prophylaxis.