The primary ingredient in traditional Italian pesto sauce is basil. This aromatic herb is blended with garlic, pine nuts, Parmesan cheese, and olive oil to create the signature flavor of pesto. The combination of fresh basil with these ingredients results in a vibrant green sauce that is often served with pasta, bread, or used as a condiment. While there are many variations of pesto that may include other herbs or nuts, the classic Genoese pesto remains based on fresh basil, highlighting its importance in Italian cuisine and its association with Mediterranean flavors.