The primary ingredient in pesto sauce is basil. This fragrant herb provides the distinctive green color and fresh flavor that defines traditional Italian pesto. Other ingredients typically include garlic, pine nuts, Parmesan cheese, and olive oil, which together create a rich and aromatic sauce. Pesto is often used in pasta dishes, spread on sandwiches, or drizzled over vegetables, making it a versatile addition to many recipes. Variations of pesto exist, using different herbs or nuts, but basil pesto remains the classic and most widely recognized version.