Many large-scale oceanic phenomena, e.g. the Gulf Stream, are driven by turbulent eddies which themselves exist on lengthscales on the order of 100km (mesoscale). The fact that such small-scale turbulent structures drive the large-scale ocean circulation gives rise to one of the greatest problems in geophysical fluid dynamics. The equations governing geophysical fluid flow are too complex to solve analytically, and we must therefore employ numerical models which solve the governing equations on a discrete grid. However, in order to numerically resolve the important turbulent flows, we typically require grid-scales on the order of 1km. Doing this is often computationally unfeasible, and we must therefore solve the governing equations on a coarse grid which is unable to capture the effects of small-scale flows. The solution is to define a parameterisation to be included in a coarse-grid model, which accounts for the effects of the turbulent eddies on the large-scale flow. I will describe the numerous methods that have been invoked to define eddy parameterisations, and outline my own research in this area.