Plant cell walls provide us with food, clothing, shelter, and energy. Cell walls make up most of the fruits, vegetables, and grains that we eat; wood and cotton fibers are almost entirely composed of cell wall material; and plant cell walls represent promising material for next-generation biofuels and renewable biomaterials like bioplastics. However, modifying plant cell walls by traditional breeding or biotechnology often decreases plant yield. This is because plants sense changes to the cell wall by largely unknown mechanisms, called “cell wall signalling” and plants often respond to cell wall signals by limiting their growth. Modifying plant cell walls for improved biomass production or pathogen resistance may inadvertently activate these pathways. By understanding the mechanisms of cell wall signalling, it may be possible to improve plant cell walls without decreasing yield. This work is important for current and future challenges in Canada, including agricultural sustainability, renewable energy production, and food security.