Display omitted •The cell wall is a biomechanical construct and cell surface sensor which responds to growth and stress cues.•Mechano-sensors at the plasma membrane modulate wall properties through feed-back loops.•Walls modulate growth, development and determine the functional specialisation of cells.•Pectins play crucial roles in wall organisation and mechanics.•Diets rich in fibre (mainly walls and resistant starches) improve health outcomes. The complexity and recalcitrance of plant cell walls has contributed to the success of plants colonising land. Conversely, these attributes have also impeded progress in understanding the roles of walls in controlling and directing developmental processes during plant growth and also in unlocking their potential for biotechnological innovation. Recent technological advances have enabled the probing of how primary wall structures and molecular interactions of polysaccharides define their biomechanical (and hence functional) properties. The outputs have led to a new paradigm that places greater emphasis on understanding how the wall, as a biomechanical construct and cell surface sensor, modulates both plant growth and material properties. Armed with this knowledge, we are gaining the capacity to design walls ‘fit for (biotechnological) purpose’!