The biofilm mode of life is by many scientists acknowledged as a successful, bacterial survival strategy in hostile environments. When bacteria invade their hosts, they encounter harsh conditions such as low levels of iron, oxidative stress, macerating enzymes, phagocytic cells, and host-derived as well as administered antimicrobials. Experimental evidence has accumulated over the years showing that biofilms tolerate antimicrobial properties of the immune system and antibiotics. This multifaceted tolerance relies to a certain extend on general resistance mechanisms including efflux pumps and enzymatic modifications in addition to innate tolerances offered by integral structure-functions of the biofilm.