Bacterial macrofibers are multicellular structures produced by certain cultures of rod-shaped cells when cells do not separate from one another after septation. Chains of cells arise that twist as they grow. This twisting is thought to reflect either the geometry of assembly of the cell wall polymers or some aspect of their anisotropic behaviour after insertion into the wall. The degree and direction of twisting is controlled by genetic and physiological factors such as growth temperature and the concentration of certain ions and other compounds in the growth medium. Twisting is ultimately responsible for a shape deformation of the cells into double-strand helical forms. The mechanical basis for shape determination and eventually macrofiber morphogenesis involves a folding process, the touching of elongating structures to themselves, blocked rotation, and shape deformation. In normal growth medium, time-lapse films reveal that writhing motions which lead to increased bending result in touching. In media of increased viscosity, bending is suppressed although elongation and rotation are unaffected. Folding occurs but now as a result of buckling. The forces responsible for both processes derive from g–, wth and interaction of the cell surface with the growth medium. The helical shape, once established, is heritable. Whether the shape becomes “set” by cross-linking or other modification of the peptidoglycan remains to be determined. From the perspective of materials science, macrofibers represent a new biodegradable fiber, the mechanical properties of which are governed by cell wall peptidoglycan. Both peptidoglycan and the other major cell wall polymer, teichoic acid, contain many reactive groups to which new constituents can be attached. Thus, there is now the potential to create a range of new materials using bacterial cells as the structural backbone.