The role of bacteria in the pathogenesis of chronic, nonhealing wounds is unclear. All wounds are colonized with bacteria, but differentiating colonizers from invading organisms is difficult, if not impossible, at the present time. Furthermore, robust new molecular genomic techniques have shown that only 1% of bacteria can be grown in culture; anaerobes are especially difficult to identify using standard culture methods. Recent studies utilizing microbial genomic methods have demonstrated that chronic wounds are host to a wide range of microorganisms. New techniques also show that microorganisms are capable of forming highly organized biofilms within the wound that differ dramatically in gene expression and phenotype from bacteria that are typically seen in planktonic conditions. The aim of this review is to present a concise description of infectious agents as defined by new molecular techniques and to summarize what is known about the microbiology of chronic wounds in order to relate them to the pathophysiology and therapy of chronic wounds.