This dish originated in Provence, in the south of France. Traditionally it contains eggplant, zucchini, tomatoes, and onions, sauteed separately and then and stirred together, with garlic, parsley, and thyme. Bell peppers and mushrooms are frequent additions, along with the local herbs (rosemary, sage, oregano, marjoram, and savory.)

Modern variations may add other ingredients, roast or bake the vegetables, or even microwave them. Sometimes ratatouille is presented as a thick stew or even a soup. It is usually a vegan dish, but some recipes add chicken, meat, or seafood, and many suggest serving it with Parmesan cheese on top.