Although rats are a much maligned species, it appears that their intelligence has been underestimated. This paper surveys evidence of cognition in rats from traditional categories (e.g. temporal and numerical competence) as well as from less ordinary test situations (e.g. transitive inference; recognition of individual humans). Although rats may not approach cognitive tasks using strategies observed in human subjects, they are frequently successful on their own terms. Indeed, rats are adept at exploiting procedural loopholes and confounded variables overlooked by human test designers. While not lending itself to the conventional classification of intelligence, this form of 'intellectual optimal foraging' may be an apt general description of the rat's cognitive prowess.