The primary ingredient in tomato sauce is ripe tomatoes. When making traditional tomato sauce, tomatoes are cooked down to create a thick, flavorful base. This process often includes simmering with various seasonings such as garlic, onions, and herbs to enhance the natural sweetness and acidity of the tomatoes. Different regions and cuisines may include additional ingredients like olive oil, wine, or vegetables. The versatility of tomato sauce makes it a staple in many dishes, especially in Italian cuisine, where it is commonly used in pasta, pizza, and stews.