Traditionally, cows have to be fed only on grass or hay. Only natural whey culture is (allegedly) allowed as a starter, together with calf rennet. The only additive allowed is salt. The product is aged an average of two years. The cheese is produced daily, and it can show a natural variability.
The name is trademarked, and in Italy there is a legal exclusive control exercised over its production and sales by the Parmigiano-Reggiano cheese Consorzio (created by a governmental decree).
See also: List of cheeses