“…[11,3,10,26]), or balance laws (e.g. [29,22]), and has recently being applied to problems that are classified under the domain of hyperbolicparabolic systems (e.g [13,20,21,4]). The objective of this work is to systematize the derivation of relative entropy identities, referring to (1.1) as a unifying framework, in order to connect the relative entropy theory with its natural framework, the L 2 theory of hyperbolic-parabolic systems of Kawashima [18] and the developments on Green functions by Liu-Zeng [30], and, even further, to exhibit the intimate connection of this method with the framework of thermodynamics.…”