 This shows how Shannon’s theory of information and Boltzmann’s notion of entropy are rooted in more fundamental mathematical concepts. The notions of a set of messages or a set of micro states are specializations of the more general mathematical concept of a set. The concept of information already exists on this more fundamental level. Although many open questions still remain, specifically in the context of the relation between information theory and physics, perspectives on a unified theory of information now look better than at the beginning of the twenty-first century. 