The primary ingredient in the traditional dish 'ratatouille' is eggplant (aubergine). Ratatouille is a classic Provençal vegetable dish originating from the south of France, showcasing vibrant, garden-fresh ingredients. The dish typically consists of a mix of vegetables, including tomatoes, zucchini, bell peppers, onions, and, of course, eggplant, all cooked together with olive oil and spices. The preparation can vary, with some recipes emphasizing a layered presentation and others promoting a more rustic, stewed texture. Ratatouille embodies the flavors of summer and reflects the principles of Mediterranean cuisine, focusing on fresh produce and healthy cooking methods.