Judging a person as a friend or foe, a mushroom as edible or poisonous, or a sound as an l or r are examples of categorization problems. This chapter considers the relative merits of four basic types of category learning models: rule-, prototype-, exemplar-, and cluster-based models. The history of model progression is marked by descendant models displaying increasingly sophisticated processing mechanisms that can manifest the behaviors of ancestral models. These four basic model types are related to the computations performed by four candidate learning systems in the human brain, which rely on prefrontal cortex, posterior occipital cortex, the striatum, and the medial temporal lobes. One issue raised is whether the prefrontal cortex and posterior occipital cortex support true learning systems or are better viewed as supporting general cognitive and perceptual abilities. Use of well-specified cognitive models can help answer related theoretical questions, such as how multiple learning systems contribute to categorization behavior.