This book stresses the role of uncorrelated exchange of properties between macroscopic systems and their surroundings as the only source of dynamic irreversibility. To that end, fundamentals of statistical thermodynamics extended to the non-equilibrium are worked out carefully. The principles are then applied to selected problems in classical fluid dynamics. Transport coefficients are first derived from basic laws. This is followed by a full discussion of transitions to dissipative structures in selected systems far removed from equilibrium (B‚nard and Taylor vortices, calculation of the critical Reynolds number for transition to turbulence in Poiseuille flow). The final part focuses on interaction of matter with light. Fundamentals are extended towards quantum-mechanical systems. Applied to coherent radiation and its interaction with matter, the proposed thermodynamic treatment introduces an original discussion into the quantum nature of micro-physics.The book questions and reconsiders a deeply rooted paradigm in macroscopic dynamics concerning the cause of irreversibility. The new proposal is illustrated by application to a couple of well documented non-equilibrium domains, namely fluid dynamics and laser physics.