Parmesan (Italian: Parmigiano Reggiano, pronounced [parmiˈdʒaːno redˈdʒaːno]) is an Italian hard, granular cheese produced from cow's milk and aged at least 12 months. It is a grana-type cheese, along with Grana Padano, the historic Granone Lodigiano [it], and others.

The term Parmesan may refer to either Parmigiano Reggiano or, when outside the European Union and Lisbon Agreement countries, a locally produced imitation.

Parmigiano Reggiano is named after two of the areas which produce it, the Italian provinces of Parma and Reggio Emilia (Parmigiano is the Italian adjective for the city and province of Parma and Reggiano is the adjective for the province of Reggio Emilia); it is also produced in the part of Bologna west of the River Reno and in Modena (all of the above being located in the Emilia-Romagna region), as well as in the part of Mantua (Lombardy) on the south bank of the River Po.

The names Parmigiano Reggiano and Parmesan are protected designations of origin (PDO) for cheeses produced in these provinces under Italian and European law. Outside the EU, the name Parmesan is legally used for imitations, with only the full Italian name unambiguously referring to PDO Parmigiano Reggiano. A 2021 press release by the Italian farmer-rancher association Coldiretti reported that, in the United States, 90% of "Italian sounding" cheese sold as parmesan, mozzarella, grana, and gorgonzola was produced domestically.^{[better source needed]}

Parmigiano Reggiano, among others, has been called "king of cheeses".

The name is legally protected in the European Union and, in Italy, exclusive control is exercised over the cheese's production and sale by The Consortium of Parmigiano Reggiano, which was created by a governmental decree. Each wheel must meet strict criteria early in the aging process, when the cheese is still soft and creamy, to merit the official seal and be placed in storage for aging. Because it is widely imitated, Parmigiano Reggiano has become an increasingly regulated product, and in 1955 it became what is known as a certified name (which is not the same as a brand name). In 2008, an EU court determined that the name Parmesan in Europe only refers to Parmigiano Reggiano and cannot be used for imitation Parmesan. Thus, in the European Union, Parmigiano Reggiano is a protected designation of origin (PDO); legally, the name refers exclusively to the Parmigiano Reggiano PDO cheese manufactured in a limited area in northern Italy. Special seals identify the product as authentic, with the identification number of the dairy, the production month and year, a code identifying the individual wheel, and stamps regarding the length of aging.

The English name parmesan is borrowed from French parmesan, earlier parmisan, in turn borrowed from Italian parmigiano. In French, it is first attested as a name for the cheese in 1414, and in English, in 1519. The regular English pronunciation is [ˈpɑː(ɹ).məˌzɑːn] but in US English it is often pronounced as the "hyper-French" [ˈpɑː(ɹ).məˌʒɑːn], using the French sound /ʒ/ (not used in this word in French) to represent the Italian sound /dʒ/.

All producers of Parmigiano Reggiano belong to the Consorzio del Formaggio Parmigiano Reggiano (lit. 'Parmigiano Reggiano Cheese Consortium'), which was founded in 1928. Besides setting and enforcing the standards for the PDO, the Consorzio also sponsors marketing activities.