<p>Abstract rules are central to human language, allowing for the generalization of grammatical rules to novel contexts. However, the evolutionary origin of the ability to learn and generalize these rules is unclear, and evidence for these capacities in nonhuman primates is equivocal. In a three-alternative forced-choice task, rhesus macaques and human participants learned to discriminate between sequences of trial-unique, colored stimuli based on three abstract rules ('ABA’, ‘AAB’ or ‘BAA’), demonstrating that, like humans, monkeys can learn and generalize abstract rules. However, follow-up testing demonstrated that unlike humans, monkeys learned slowly, showed limited cognitive flexibility in rule switching, and did not generalize across stimulus domains (from color to shape), suggesting that monkeys acquire more limited, context-specific representations. These results suggest that a critical open question regarding the uniqueness of human cognition is not only <i>what</i> animals are able to learn, but <i>how</i> they learn and represent abstract rules.</p>