Direct observations, in natural and pathogenic ecosystems, have shown that > 99% of bacteria grow in matrixenclosed biofilms adherent to surfaces or interfaces.These sessile bacterial communities are the basic unit of metabolic activity in ecosystems, and the basic unit of pathogenicity in the chronic bacterial infections that now predominate in modern medicine and Dentistry.Within these communities cells communicate by means of diffusible signals, and by means of signals enclosed in vesicles and complex tubular systems, so that the biofilm is a single functional unit within which metabolic and ecological relationships are highly organized and well coordinated.