Clam chowder is any of several chowders containing clams and broth. Along with the clams, diced potato is common, as are onions, which are occasionally sautéed in the drippings from salt pork or bacon. Celery is frequently used. Other vegetables are uncommon, but small carrot strips might occasionally be added, primarily for color. A garnish of parsley serves the same purpose. Bay leaves are also sometimes used as a garnish and flavoring. It is believed that clams were added to chowder because of the relative ease of harvesting them.

Clam chowder is often served in restaurants on Fridays in order to provide a seafood option for those who abstain from meat every Friday, which once was a requirement for Catholics before liturgical changes in Vatican II. Though the period of strict abstinence from meat on Fridays was reduced to Lent,the year-round tradition of serving clam chowder on Fridays remains.