The word 'Ratatouille' actually comes from the french term "touiller," which means to toss food.
I have often been asked whether the dish is real or just made up for the Disney movie, well it is real; Ratatouille originated in the area around present day Nice. It was originally a meal made by poor farmer's (in essence it started out life as a peasant dish), and was prepared in the summer with fresh summer vegetables.
The original and simplest form of Ratatouille only uses the following ingredients: courgettes (zucchini), tomatoes, green and red peppers (bell peppers), onions, and garlic. You can find some great recipes here.
Today aubergine (eggplant) is usually added to the list of ingredients.
There are numerous version of Ratatouille and this site will show the the best of the worlds versions for you to try at home.
I even have a recipe which is close to the Disney ratatouille recipe.