 The emergence of a coherent theory to measure information quantitatively in the twentieth century is closely related to the development of the theory of computing. Central in this context are the notions of Universality, Turing equivalence and Invariance: because the concept of a Turing system defines the notion of a universal programmable computer, all universal models of computation seem to have the same power. This implies that all possible measures of information definable for universal models of computation (Recursive Functions, Turing Machine, Lambda Calculus etc.) are invariant modulo an additive constant. This gives a perspective on a unified theory of information that might dominate the research program for the years to come.