Microbial infections constitute an important reason for medical treatment, especially in dentistry. Ideas about the role played by bacteria in the development of diseases have changed steadily during the past centuries. At the present time much attention is being devoted to the role of biofilms due to their illness-causing influence with respect to stitches on hard tissue and on oral implants, knee-, hip-, and voice prostheses. In biofilms, bacteria function and communicate in organized extrapolymeric structures, attached to a surface. Biofilms provide bacteria with protection against the host’s immune system and antibacterial chemicals. By gaining insights into the creation and functioning of biofilms, it will be possible to develop better antibacterial therapies.