Clam chowder is any of several chowder soups containing clams and broth. In addition to clams, common ingredients include diced potatoes, onions, and celery. Other vegetables are not typically used, but small carrot strips or a garnish of parsley might occasionally be added primarily for color. A garnish of bay leaves adds both color and flavor. It is believed that clams were used in chowder because of the relative ease of harvesting them. Clam chowder is usually served with saltine crackers or small, hexagonal oyster crackers.
The dish originated in the Eastern United States, but is now commonly served in restaurants throughout the country, particularly on Fridays when American Catholics traditionally abstained from meat. Many regional variations exist, but the two most prevalent are New England or "white" clam chowder and Rhode Island / Manhattan or "red" clam chowder.The earliest-established and most popular variety of clam chowder, New England clam chowder, was introduced to the region by French, Nova Scotian, or British settlers, becoming common in the 18th century. The first recipe for another variety, Manhattan clam chowder, known for using tomatoes and its consequently distinctly red coloring, was published in 1934. In 1939, the New England state of Maine debated legislation that would outlaw the use of tomatoes in chowder, thereby essentially prohibiting the "Manhattan" form.One claim to traditional Rhode Island clam chowder is a red chowder with a tomato broth base and potatoes but - unlike Manhattan style - Rhode Island's clam chowder has no chunks of tomato and does not contain other vegetables. Its origins are reportedly Portuguese and it was commonly served with clamcakes.
Another tradition has a clam chowder made with clear broth which is common along the New England coast from eastern Connecticut to southwestern Rhode Island. In southwestern Rhode Island, it is sometimes called "South County Style" referring to the colloquial name of Washington County, Rhode Island, where it allegedly originated. In other parts of New England, it contains quahogs, broth, potatoes, onions, and bacon