The holy trinity is the Cajun and Louisiana Creole variant of mirepoix: onions, bell peppers, and celery in roughly equal quantities. This mirepoix is the base for much of the cooking in the regional cuisines of Louisiana. Variants use garlic, parsley, or shallots for one of the three.
The preparation of Cajun/Creole dishes such as étouffée, gumbo, and jambalaya all start from this base.
Origin of the name 
The name is an allusion to the Christian doctrine of the Trinity. Louisiana is a strongly Roman Catholic region.
The term is first attested in 1981 and was probably popularized by Paul Prudhomme.
In other cuisines 
The term has occasionally been used to describe various other triples of important ingredients in a variety of cuisines.
See also 
- ^ Patricia Perrine, "Louisiana French Foodways: The Perpetuation of Ethnicity in the Lafourche Area", North American Culture 2:7 (1985) Google Books
- ^ Craig Claiborne, "Claiborne Shares 'Catfish Memories'", Florence Times, November 26, 1981, p. 20 Google News
- ^ Craig Claiborne, A feast made for laughter, 1982, p. 30 Google Books