Processed cheese (also known as process cheese; related terms include cheese food, prepared cheese, cheese product, and/or government cheese) is a product made from cheese mixed with an emulsifying agent (actually a calcium chelator). Additional ingredients, such as vegetable oils, unfermented dairy ingredients, salt, food coloring, or sugar may be included. As a result, many flavors, colors, and textures of processed cheese exist. Processed cheese typically contains around 50–60% cheese and 40–50% other ingredients.

Processed cheese was first developed in Switzerland in 1911, when Walter Gerber and Fritz Stettler, seeking a cheese with longer shelf life and influenced by fondue and cheese sauces, added sodium citrate to melted Emmentaler cheese and found that the emulsified cheese sauce could be re-cooled into a solid again. Shortly after, in 1916, Canadian-American businessman James L. Kraft applied for the first U.S. patent covering a new method of storing cheese, which halts the maturation process by sterilization.

Processed cheese has several technical advantages over natural cheese, including a far longer shelf life, resistance to separating when cooked (meltability), and a uniform look and physical behavior. Its mass-produced nature also provides a dramatically lower cost than conventional cheesemaking, and enables industrial-scale production volumes, lower distribution costs, a steadier supply, and much faster production time compared to traditional cheeses.

Because processed cheese does not separate when melted, it is used as an ingredient in a variety of dishes. Unlike some unprocessed cheeses, heating does not alter its taste or texture.^{[citation needed]}

Processed cheese is made with the goal of being meltable without the fat separating from the protein. A traditional cheese consists of individual fat globules trapped in a network of casein, with calcium holding the casein molecules together. With prolonged heating, the typical result is a lumpy combination of protein gel and liquid fat on top. Processed cheese adds a calcium-sequestering agent, often mistakenly called an "emulsifier" ("emulsifying salt" and "emulsifying agent" are correct, however), to stop calcium from being able to hold this casein network together. Smaller groups of linked casein molecules are then able to better mix into the fat when melted, forming microscopic droplets instead of large lumps. Common calcium-sequestering agents include sodium phosphate, potassium phosphate, tartrate, and citrate. (Tartaric acid found in wine is the original calcium-sequestering agent used in Swiss fondue.)

The longer shelf-life is not directly because of the emulsifying agent, but because it allows existing heat-based sterilization methods, such as canning, to be applied to the cheese without forming lumps.

Processed cheese is often sold in blocks and packs of individual slices, often separated by wax paper, or with each slice individually wrapped by machine. Processed cheese was initially sold in unpressurized cans; some is still sold this way.

In the United Kingdom, processed cheese is typically sold in individually wrapped slices, often referred to as "singles" (in reference to Kraft singles, despite the branded product not being typically available in the UK.) Sometimes, adjectives like "cheesy" are used in the name of "singles" to circumvent laws regarding what can be referred to as cheese. Dairylea and The Laughing Cow are leading brands.