In bacteria, the rigid external cell wall (CW) and the intracellular actin-like (MreB) cytoskeleton are major determinants of cell shape. Synthesis and chemical composition of the CW, a three dimensional polymer network that is one of the most prominent targets for antibiotics, are well understood. However, despite decades of study, little is known about the complex CW ultrastructure and the molecular mechanisms that control cell shape in time and space. MreB homologues assemble into dynamic membrane-associated structures thought to control shape by serving as organizers for the movement and assembly of macromolecular machineries responsible for CW biogenesis. However, the mechanistic details used by the MreB cytoskeleton to fulfill this role remain to be elucidated. We will combine powerful genetic tools available in the model Gram-positive bacterium Bacillus subtilis with modern high-resolution fluorescence microscopy techniques and atomic force microscopy (AFM) to study the role of the MreB cytoskeleton and CW synthesis proteins in cell shape determination and maintenance. Additionally, the role of mechanical forces in the control of CW organization will be evaluated.