Add the Greek yogurt, mayonnaise, parsley, basil, chives, garlic, lemon juice, olive oil, salt, and black pepper to a food processor or blender.
Blend until the herbs are finely chopped and the dip is smooth and creamy.
Scrape down the sides of the bowl and blend again if needed.
Taste and adjust with additional lemon juice, salt, or pepper.
If making a dressing, blend in 1-3 tablespoons of water, milk, or buttermilk until you reach your desired consistency.
Transfer to a serving bowl and refrigerate for 30 minutes before serving for the best flavor.