This paper is a short review of the recent developments in understanding trends in electro-catalysis of the oxygen reduction reaction (ORR). Our focus is on atomic scale simulations at the density functional theory level. First, we investigate the models and the approximations that have been assumed, and thence we reach the conclusion that trends in electrocatalysis are well captured by only considering binding energies of reaction intermediates to the catalyst surface. We show, assuming a simple and very likely series of intermediates, existence- of a universal scaling relation common to all ORR catalysts, which defines the overpotential.