Iron is an essential metal for most biological organisms. However, if not tightly controlled, iron can mediate the deleterious oxidation of biomolecules. This review focuses on the current understanding of the role of iron in the deleterious oxidation of various biomolecules, including DNA, protein, lipid, and small molecules, e.g., ascorbate and biogenic amines. The effect of chelation on the reactivity of iron is also addressed, in addition to iron-associated toxicities. The roles of the iron storage protein ferritin as both a source of iron for iron-mediated oxidations and as a mechanism to safely store iron in cells is also addressed.