A synopsis of some basic concepts in equilibrium and non-equilibrium thermodynamics and statistical mechanics is presented. It is stressed that no theory of non-equilibrium phenomena of the scope of equilibrium macroscopic theory is currently available and some of the difficulties associated with constructing a broadly valid theory of irreversible processes are discussed. Solid results are, however, now available in two limiting timescales regimes. These are the traditional “slow variable” regime important for macroscopic transport phenomena and an opposite and non-traditional “fast variable” regime important for molecular processes in condensed phases. These two limiting regimes are described and contrasted and the very different concepts of friction which emerge in these regimes are compared.