Most oceanic turbulence and eddies originate from the development of instabilities resulting from the combined effects of density gradients and fast rotation. We present here numerical Large-Eddy Simulations (LES) of high-Reynolds number turbulent flows of oceanic interest. We first investigate the effects of solid-body rotation on free-shear flows, wall-bounded flows, and homogeneous turbulence, and show the drastic modification of the flow topology. We then show how LES techniques can be applied to the computation of oceanic mesoscale eddies resulting from various instability mechanisms such as baroclinic instability and convective instability.