The main ingredient in pesto is basil. Traditional basil pesto, originating from Italy, is made by blending fresh basil leaves with garlic, pine nuts, Parmesan cheese, and olive oil. The combination of these ingredients creates a fragrant and flavorful sauce, commonly used in pasta dishes, sandwiches, or as a dip. The vibrant green color and fresh taste of basil are quintessential to the sauce's identity. While variations exist that substitute ingredients like walnuts or different greens, basil remains the classic choice, providing pesto with its signature flavor profile and quality that many people love.