Cocktail sauce is a chilled condiment for shellfish, made from a ketchup or chili sauce base mixed with horseradish, lemon juice, and often Worcestershire sauce. It emerged in the early 20th century in the United States as the standard accompaniment to shrimp cocktail and remains most associated with North American seafood service. The horseradish gives it a sharp, pungent bite that cuts through the richness of shrimp, crab, lobster, and oysters; some versions add hot sauce for extra heat. It's also used as a dip for fried seafood or stirred into dishes like deviled eggs.