Cellulose biosynthesis has recently been established for a variety of bacteria of diverse origin at the phenotypic and genetic levels. Novel regulatory pathways, which involve the second messenger bis-(3',5') cyclic diguanylic acid and several proteins with the GGDEF domain, participate in the regulation of cellulose biosynthesis. The biological significance of cellulose production in environmental, commensal and pathogenic bacteria is only punctually resolved. This review summarizes current knowledge on cellulose biosynthesis, its regulation and biological function.