The origin of the dish and its name is somewhat disputed. One claim is that the dish was created out of a mistake made by a fourteen-year-old assistant waiter Henri Charpentier in 1895 at the Maitre at Monte Carlo's Café de Paris. He was preparing a dessert for the Prince of Wales, the future King Edward VII of the United Kingdom, and his companion Princess Suzanne (daughter of Edward, Prince of Wales, who was the son of Queen Victoria). It was his favourite meal.

Ratatouille is usually served as a side dish, but also may be served as a meal on its own (accompanied by pasta, rice or bread). Tomatoes are a key ingredient, with garlic, onions, courgettes (zucchini), aubergine (eggplant), poivron (bell peppers), carrot, marjoram and basil, or bay leaf and thyme, or a mix of green herbs like herbes de Provence. There is much debate on how to make a traditional ratatouille. One method is to simply sauté all of the vegetables together. Some cooks, including Julia Child, insist on a layering approach, where the eggplant and the zucchini are sautéed separately, while the tomatoes, onion, garlic and bell peppers are made into a sauce.