The cyclic nucleotide cyclic di-guanosine-monophosphate (c-diGMP) was recognized in the 1980s as a signaling compound that is involved in controlling the condensation of glucose moieties into cellulose polymers. More recent data from several different bacterial species now suggest that c-diGMP might have a general role as secondary messenger in modulating bacterial growth on surfaces by regulating cellular adhesion components and preparing cells for cell-cell and cell-surface interactions.