The main ingredient in a traditional pesto is basil. Pesto is a sauce that originated in Genoa, Italy, and is typically made by blending fresh basil leaves with garlic, pine nuts, parmesan cheese, and olive oil. The vibrant green color and aromatic flavor of basil gives pesto its distinctive taste and character. While traditional pesto uses these specific ingredients, variations can incorporate different herbs, nuts, or cheeses, adapting to local flavors. Pesto is often used as a pasta sauce, spread on bread, or as a seasoning for various dishes, contributing to its popularity in Italian cuisine.