Pewter is a malleable metal alloy consisting of tin (85–99%), antimony, copper (2%), bismuth, and sometimes silver. In the past it was an alloy of tin and lead, but most modern pewter, in order to prevent lead poisoning, is not made with lead. Pewter has a low melting point, around 170–230 °C (338–446 °F), depending on the exact mixture of metals. The word pewter is probably a variation of "spelter", a term for zinc alloys.

An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, opacity, and luster, but may have properties that differ from those of the pure metals, such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength.