The primary ingredient in a traditional pesto is basil. This fragrant herb forms the base of the classic Italian sauce, which is often combined with other ingredients like garlic, pine nuts, Parmesan cheese, and olive oil to create a rich and aromatic blend. The combination of fresh basil and these complementary ingredients results in a vibrant green sauce that can be used in various dishes, including pasta, sandwiches, and salads. While traditional pesto hails from the Liguria region of Italy, variations exist, incorporating different herbs or nuts, yet basil remains the signature flavor that defines the dish.