Publisher Summary Foraging is a fundamental behavior that defines animals. There are many ways to forage, but many of them can be placed into the framework of optimality theory, which is not limited to foraging behavior—almost any decision can be optimized—but it has perhaps had the biggest impact there. When considering optimality and animal behavior, or optimality and any product of evolution, it is important to understand that many constraints can prevent optimal outcomes in nature. In the study of foraging, optimality models have classically been applied to two large areas: decisions about where to forage (patch choice) and decisions about what to eat (prey choice). Both of these areas are based on several assumptions, including the fact that animals are likely to have sampled their environment and be familiar with the choices on offer. The ways that animals get food are so diverse as to defy description or categorization. From fungal gardens to central place foraging (and hoarding), from antelope grazing to cheetah decisions, this diversity is both a wonderful showcase for how evolution encourages animals to convert nutrients into offspring and also a schoolhouse, teaching the importance of clear assumptions and careful experiments.