Biofilms are antibiotic-tolerant, sessile bacterial communities that occupy most moist surfaces on Earth and represent a major mode of bacterial life. Another common feature of bacterial life is exposure to bacteriophages, which are a dominant force in bacterial population control and evolution. The interaction mechanisms between biofilm-dwelling bacteria and phages are poorly understood. We are investigating the physiological response of Pseudomonas aeruginosa biofilms to lytic phage predation, and how this response affects community development and phage spread.