Microorganisms can live and proliferate as individual cells swimming freely in the environment, or they can grow as highly organized, multicellular communities encased in a self-produced polymeric matrix in close association with surfaces and interfaces. This microbial lifestyle is referred to as biofilms. The intense search over the last few years for factors involved in biofilm development has revealed that distantly related bacterial species recurrently make use of the same elements to produce biofilms. These common elements include a group of proteins containing GGDEF/EAL domains, surface proteins homologous to Bap of Staphylococcus aureus, and some types of exopolysaccharides, such as cellulose and the poly-β-1,6-N-acetylglucosamine. This review summarizes current knowledge about these three common elements and their role in biofilm development.This work was supported by the BIO2002-04542-C02 and GEN2003-20234-C06-05 grants from the Comisión Interministerial de Ciencia y Tecnología (Madrid, Spain) and grant 17/2004 from the Departamento de Educación y Cultura del Gobierno de Navarra, Spain.Peer reviewed