A diner is a small fast food restaurant that is found in the American Northeastern United States and Midwest, as well as in other states, Canada, and parts of Western Europe. Diners offer a wide range of foods, mostly American, a distinct exterior structure, a casual atmosphere, a long counter with bar stools where patrons eat their meals, and late operating hours. Diners frequently stay open 24 hours a day, especially in cities and towns with a busy bar scene or with factories with night shifts. Bar patrons seeking a post-"last call" venue to socialize and get food and shift workers leaving their factories historically provided a key part of the customer base.
From the 1920s to the 1940s, diners were usually prefabricated in factories (like a mobile home) and delivered to the restaurant site. As a result, old diners were typically narrow and small, because they had to fit onto a rail car or truck for delivery to the restaurant site. Some vintage diners have been expanded over the years, by building additions into the prefab structure. In the 2010s, many new diners are built on site instead. Diners were historically small businesses operated by the owner. In the 2010s, some diners are operated by chains.
Diners typically serve American food such as hamburgers, french fries, club sandwiches, and other simple, quick and inexpensive fare. Much of the food is grilled, as early diners were based around a grill. Coffee is the ubiquitous beverage at diners, even if it is not always of high quality. Diners often serve hand-blended milkshakes and desserts such as pies, which are typically displayed in a glass case. Classic American diners often have an exterior layer of stainless steel siding—a feature unique to diner architecture. In some cases, diners share nostalgic, retro style features also found in some restored drive-ins and old movie theatres. Some car culture enthusiasts also enjoy going to diners, such as hot rod and vintage muscle car fans.