Endothermy is fundamental to the life of mammals. Mammals must wring as many calories as possible from the foods they eat in order to provide enough energy to heat their bodies. And this is where teeth come in. ‘Mammal teeth today’ looks at the dental diversity of mammalian teeth in both marsupials and placentals. Both of these mammalian groups exhibit a variety of species and dental adaptations that explain the relationships between species richness, diet, and teeth. Mammalian teeth provide some of the finest examples of convergent evolution, which offer insights both into relationships between form and function, and into how the genes that code for tooth shape change and express themselves.