In addition to clams, common ingredients include diced potatoes, salt pork, and onions.

[4] Early documentation of "clam chowder" as we know it today did not contain milk and was thickened during cooking using crackers or stale bread.

[5] The first recipe for Manhattan clam chowder, with tomatoes and no milk, was published before 1919,[6] and the current name was attested in 1934.

As recipes for clam chowder spread throughout the United States in the 19th and 20th centuries, many regionally developed variants have arisen.

[17] Served throughout North Carolina's Outer Banks region, this simple variation of clam chowder has clear broth, bacon, potatoes, and onions.

[18][19] Minorcan clam chowder is a spicy traditional version found in Florida restaurants near St. Augustine and the northeast corner of the Sunshine State.

It has a tomato broth base, with a "secret ingredient", Spanish datil pepper, an extremely hot chili comparable to the habanero.