Many gram-positive bacteria are able to form aggregates or biofilms and resist external stress factors and some gram-positive pathogenic bacteria such as Listeria monocytogenes and Bacillus cereus may persist in the food production environment for extended periods. Most research has focussed on the gram-negative bacteria and, in general, less is known abourt the gram poritives. At present much conflicting evidence has been presented perhaps because so many internal and external factors influence the ability to adhere. Some of the present knowledge of biofilm or aggregation forming properties will presented and discussed.