Which French herbal liqueur is the signature ingredient in a Chartreuse Swizzle?

Green Chartreuse is the signature herbal liqueur in a Chartreuse Swizzle.

The drink combines Green Chartreuse with pineapple juice, lime juice, and falernum, then is swizzled with crushed ice until the outside of the glass becomes frosty. Green Chartreuse is a high-proof liqueur made by Carthusian monks from a secret recipe involving many botanicals. Its intense color and concentrated herbal flavor make it unusually prominent in mixed drinks.

Yellow Chartreuse is a separate expression: it is sweeter, milder, and lower in alcohol than the green version. Substituting it changes the balance and does not produce the classic Chartreuse Swizzle profile. The modern cocktail became especially associated with bartender Marcovaldo Dionysos and the San Francisco bar scene, where it helped introduce the liqueur to a newer generation of cocktail drinkers. Falernum contributes spice and sweetness, but it is not the defining named ingredient.