  We provide an historical perspective of how the notion of correlations has
evolved within quantum physics. We begin by reviewing Shannon's information
theory and its first application in quantum physics, due to Everett, in
explaining the information conveyed during a quantum measurement. This
naturally leads us to Lindblad's information theoretic analysis of quantum
measurements and his emphasis of the difference between the classical and
quantum mutual information. After briefly summarising the quantification of
entanglement using these and related ideas, we arrive at the concept of quantum
discord that naturally captures the boundary between entanglement and classical
correlations. Finally we discuss possible links between discord and the
generation of correlations in thermodynamic transformations of coupled harmonic
oscillators.
