crystallographic and spectroscopic data are shown to coalesce to the same picture of a predominant S=6 species containing the first one-electron oxidation product of two water molecules i.e. [O5O6] 3-. Progression of this form to the two-electron oxidised peroxo and three-electron oxidised superoxo forms, leading eventually to the evolution of triplet O 2 , is proposed to be the pathway Nature adopts to oxidise water. The study reveals the key electronic, magnetic and structural design features of Nature's catalyst which facilitates water oxidation to O 2 under ambient conditions.