Bacterial cell shape is important for cell viability and many biological functions such as motility, host invasion, and biofilm formation. Rod-like Gram-negative bacteria such as Escherichia coli control their macroscopic cylindrical shape with high precision by expanding and remodeling the peptidoglycan cell wall. Many of the major components required for cell-wall synthesis and cell-shape generation are known. However, only recently have we gained first insights into their spatio-temporal regulation. Specifically, we found that the bacterial cytoskeleton MreB is dynamically coupled to cell-wall synthesis during elongation of rod-like bacteria, suggesting that MreB filaments play an important role in shaping the cell. At the same time, the cell-wall remodeling machinery reacts to other cues and signals, such as the progression of the cell cycle, changes in growth environment, and mechanical stress. I will give an overview of our current understanding of how physical cues shape the cell, and I will outline future directions towards understanding the determinants of cell-wall expansion using combined single-molecule microscopy, modeling, and classical molecular biology.