A submarine sandwich, also known as a hero sandwich, Italian Sandwich, sub, hoagie, torpedo or grinder amongst many regional naming variations, is a sandwich that consists of a long roll of Italian or French bread, split lengthwise either into two pieces or opened in a "V" on one side, and filled with a variety of meats, cheeses, vegetables, seasonings, and sauces. The sandwich has no standardized name, and many U.S. regions have their own names for it; one study found 13 different names for the sandwich in the United States. The usage of the several terms varies regionally but not in any pattern, as they have been used variously by the people and enterprises who make and sell them. The terms submarine and sub are widespread and not assignable to any certain region, though many of the localized terms are clustered in the northeast United States, where most Italian Americans live.

The sandwich originated in several different Italian American communities in the Northeastern United States from the late 19th to mid 20th centuries. Portland, Maine claims to be the birthplace of the "Italian sandwich" and it is considered Maine's signature sandwich. The popularity of this Italian-American cuisine has grown from its origins in Connecticut, Pennsylvania, Delaware, New York, New Jersey, and Massachusetts to most parts of the United States, and with the advent of chain restaurants, is now available in many parts of the world. In Europe it would simply be known as a baguette, or a ciabatta, named after traditional breads long baked in France and Italy.