From wikipedia: Most countries use the spelling aluminium (with an i before -um). In the United States, this spelling is largely unknown, and the spelling aluminum predominates. The Canadian Oxford Dictionary prefers aluminum, whereas the Australian Macquarie Dictionary prefers aluminium. The International Union of Pure and Applied Chemistry (IUPAC) adopted aluminium as the standard international name for the element in 1990, but three years later recognized aluminum as an acceptable variant. Hence their periodic table includes both. IUPAC officially prefers the use of aluminium in its internal publications, although several IUPAC publications use the spelling aluminum.