The primary ingredient in ratatouille is vegetables, particularly eggplant, zucchini, bell peppers, tomatoes, and onions. Ratatouille is a traditional Provençal dish that highlights the vibrant flavors of these fresh, seasonal vegetables. The ingredients are typically sautéed or roasted together with herbs like thyme and basil, allowing their flavors to meld beautifully. This dish is both rustic and elegant, showcasing the essence of Mediterranean cooking. Ratatouille can be served as a side dish, main course, or even as a filling for other dishes, demonstrating its versatility and appeal.