The teeth of mammals are the key interface between food and animal – where the rubber meets the road. Mammals generally use their teeth for mechanical processing, thereby facilitating and increasing rates of ingestion, digestion and fermentation. The various foods eaten by mammals respond to bite forces in different ways: some foods fracture easily, while others resist cracks propagating through them. In addition, some foods must be broken down to small pieces for effective energy and nutrient extraction; others merely need to be small enough to swallow. The most effective tooth morphology therefore varies with the mechanical properties of the food. Tooth shape can help to determine the typical food sources consumed by mammals at a given fossil locality, which in turn informs the broad environmental conditions and community structure once present at the site. In this chapter, we examine the ways in which mammalian tooth morphology can serve as an indicator of diet and thus past environments by examining the materials science of foods and the functional morphology of mammal teeth.