Cheddar cheese (or simply cheddar) is a natural cheese that is relatively hard, off-white (or orange if colourings such as annatto are added), and sometimes sharp-tasting. Cheddar originates from the English village of Cheddar in Somerset.

Cheddar cheese is produced all over the world, and cheddar cheese has no protected designation of origin either in the United Kingdom or the European Union. In 2007, the protected designation of origin name "West Country Farmhouse Cheddar" was registered in the EU and (after Brexit) the UK, defined as cheddar produced from local milk within Somerset, Dorset, Devon and Cornwall and manufactured using traditional methods. Protected Geographical Indication (PGI) was registered for Orkney Scottish Island Cheddar in 2013 in the EU, which also applies under UK law. Globally, the style and quality of cheeses labelled as cheddar may vary greatly, with some processed cheeses being packaged as "cheddar". Furthermore, certain cheeses that are similar in taste and appearance to Red Leicester are sometimes marketed as "red cheddar".

Cheddar is the most popular cheese in the UK, accounting for 51% of the country's £1.9 billion annual cheese market. It is the second-most popular cheese in the US behind mozzarella, with an average annual consumption of 10 lb (4.5 kg) per capita. The US produced approximately 3,000,000,000 lb (1,300,000 long tons; 1,400,000 tonnes) of cheddar cheese in 2014, and the UK produced 258,000 long tons (262,000 tonnes) in 2008.