Natural biostimulants for sustainable and resilient agriculture? Microalgae may be the answer. They are photosynthetic single-celled organisms that can improve nutrient uptake, protect against pests and diseases, and increase resistance to environmental stresses such as hail, water bombs, or drought. Their large-scale use is not yet possible, but new opportunities related to a circular economy model based on agroindustrial waste recycling could prove to be the key tosustainable agriculture that can address the effects of climate change.