Robert Rupert is well-known as an vigorous opponent of the hypothesis of extended cognition (HEC). His Cognitive Systems and the Extended Mind is a first-rate development of his “systems-based” approach to demarcating the mind. The results are impressive. Rupert’s account brings much-needed clarity to the often-frustrating debate over HEC: much more than just an attack on HEC, he gives a compelling picture of why the debate matters.