The primary ingredient in pesto is basil, specifically fresh basil leaves. This classic Italian sauce blends basil with other ingredients, including garlic, pine nuts, Parmesan cheese, and olive oil. The basil provides a strong, aromatic flavor that is characteristic of pesto. Traditionally, pesto is made using a mortar and pestle, allowing the flavors to meld together beautifully. While the classic recipe is known as "Pesto alla Genovese," variations exist, incorporating different herbs and nuts, such as parsley or walnuts. Pesto is commonly used as a sauce for pasta, but it can also be a flavorful spread or dip.