Cellulose microfibrils containing crystalline beta-1,4-glucan provide the major structural framework in higher-plant cell walls. Genetic analyses of Arabidopsis thaliana now link specific genes to plant cellulose production just as was achieved some years earlier with bacteria. Cellulose-deficient mutants have defects in several members of one family within a complex glycosyltransferase superfamily and in one member of a small family of membrane-bound endo-1,4-beta-glucanases. The mutants also accumulate a readily extractable beta-1,4-glucan that has short chains which, in at least one case, are lipid linked. Cellulose could be made by direct extension of the glucan chain by the glycosyltransferase or, as the mutant suggests, by an indirect route which makes lipid-linked oligosaccharides. Models discussed incorporate the known enzymes and lipo-glucan and raise the possibility that different CesA glycosyltransferases may catalyse different steps.