The hippocampus has achieved an undeniable glamour as a model for the neurobiology of learning and memory. The question of its exact function in learning, however, is still a matter of controversy. Its role in spatial navigation in birds and mammals is not contested, however, and I suggest that this spatial function may offer the key to understanding the current suite of spatial and nonspatial hippocampal functions demonstrated in rodents and primates. I address these questions with comparative studies of spatial and episodic-like memory in food-storing rodents species (tree squirrels and kangaroo rats), showing that patterns of spatial learning ability predict patterns of hippocampal development and plasticity, as well as species and sex differences in hippocampal structure.