‘Teeth matter’ considers how teeth can help us understand ecology and paleontology. An organism eats its neighbour for the fuel and raw materials needed to grow, sustain itself, and reproduce. Teeth matter because they mediate between eater and eaten. The evolution of teeth provided an advantage for capturing and immobilizing prey, and chewing allowed animals to extract more fuel from each mouthful of food. Teeth are the most common vertebrate fossils found and can be used to infer the diets of past animals. Advances in dental research offer fresh insights into how teeth work, how animals use them today, and how they used them in the past.