Sophistication, a modern notion of complexity, is then discussed. This measure of "meaningful information", although popularised in science books such as "The Quark and the Jaguar" by Murray Gell-Mann, has only been formalised very recently (see "Meaningful Information" by Paul Vitanyi, http://www.cwi.nl/~paulv). The relationship of sophistication to learning is outlined, first in relation to ideal statistical inference and the minimum description length (MDL) method, then to reinforcement learning and the broader AI effort.