The first goal of this chapter is to address the suggestion to move from NSE to LSE. The second goal is to derive the LSE specifically, modelling of the turbulent forcing acting on an eddy of arbitrary size. The LSE are then shown to predict basic turbulence relations, data from measurements and numerical simulations and thermal convection. Mesoscales in the adiabatic and diabatic regime are discussed together with several results. Mesoscale diffusivity and kinetic energy are derived. Results from an OGCM are presented and compared with data of other groups. Subduction and upwelling by mesoscales are discussed. Next, the text treats Sub-mesoscales, their contributions to subduction, re-stratification and eddy compensation, destruction of potential vorticity, SM eddy kinetic energy, induced vertical velocity and coexistence of meso and sub-mesoscales.