This is a review commissioned by the EU Commission in 2009. Abstract: Serious concerns about the resistance of nosocomial, community-acquired and foodborne pathogens to antibiotics have been growing for a number of years at both national and international levels. Resistance of bacterial pathogens to antibiotics has increased worldwide, leading to treatment failures in human and animal infectious diseases. Bacteria have the capacity to adapt rapidly to new environmental conditions and can survive exposure to antimicrobials by using a battery of resistance mechanisms. The frequency of antimicrobial resistance in bacteria has increased in concert with increasing usage of antimicrobial compounds. Bacterial resistance against different types of biocides has been reported and characterised only relatively recently when compared to our understanding of antibiotic resistance. Some resistance mechanisms are common to both biocides and antibiotics. Scientific evidence from bacteriological, biochemical and genetic data does indicate that the use of active molecules in biocidal products may contribute to the increased occurrence of antibiotic resistant bacteria. The selective stress exerted by biocides may favour bacteria expressing resistance mechanisms and their dissemination. Some biocides have the capacity to maintain the presence of mobile genetic elements that carry genes involved in cross-resistance between biocides and antibiotics. The dissemination of these mobile elements, their genetic organisation and the formation of biofilms, provide conditions that could create a potential risk of development of cross-resistance between antibiotics and biocides. To date, the lack of precise data, in particular on quantities of biocides used, makes it impossible to determine which biocides create the highest risk of generating antibiotic resistance. However, horizontal gene transfer and overlapping genetic cascades of regulation that can be stimulated by external chemical compounds such as biocides arelikely triggers of bacterial resistance. In view of the large and increasing use of biocides and the continuous increase of bacterial resistance to antibiotics, data and methodologies are urgently needed to clearly characterise the risk.