Basil is the herb that is sometimes called sweet basil (AKA Italian or Genovese basil) in much of the English-speaking world. Thai basil is a relative of basil that is a traditional staple herb in Southeast Asia, but that has become popular around the world as people become more aware of Thai and Vietnamese cuisine. The two herbs do share some characteristics but are also dramatically different in many ways. Let’s compare them in the SPICEography Showdown below.
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How does basil differ from Thai basil?
Basil and Thai basil have different appearances. Basil has smooth green stems and broad, soft leaves with uniform edges. The stems of the basil plant are delicate. Thai basil has hairy purple stems and narrower, firmer leaves. The edges of the leaves look serrated. The stems of the Thai basil plant are woodier and more robust than those of the basil plant. When basil bolts it produces tiny white blossoms, while Thai basil’s flowers are pink or purple.
Basil 
Thai Basil
The flavors of basil and Thai basil differ. Basil has a mild peppery note with a hint of clove; Thai basil has a stronger spicy flavor with a concentrated anise or licorice note. Thai basil’s more intense flavor and sturdy leaves stand up better to high-heat cooking and are less likely to be hidden by spicy and pungent ingredients than the relatively mild basil.
The availability of basil and Thai basil depends on your location. Fresh basil can be found in the produce sections of many large grocery stores in the US and much of Europe. Thai basil has become easier to find outside of Asia in recent years but still is not as mainstream in many places as basil. You might not be able to find it in the average grocery store. You can find it in many Asian stores but even there it might be expensive and seasonal.
If your recipe calls for one, can you use the other?
Basil can work as a Thai basil substitute but only if you have no better options. It won’t be ideal for Southeast Asian recipes since it lacks the pungent, peppery bite of Thai basil. If you can add mint and cilantro to the dish to enhance the basil, the absence of Thai basil may not be as noticeable, but it will be easy to see otherwise.
Thai basil may work as a sweet basil substitute in some dishes — cooked ones not salads — but it won’t be ideal, and you may have to use less of it so that its stronger elements aren’t as noticeable.
When should you use basil, and when should you use Thai basil?
Basil is famous for its role in Italian dishes like Bolognese sauce and Caprese salad. You can also use fresh basil as a topping for Margherita pizza, and it is the main ingredient in traditional pesto. The mildness of basil’s flavor means that the best time to add it to a dish is at the end of the cooking time. The less exposure to heat it undergoes, the more flavor it retains.
Thai basil is used in dishes from Thailand, Cambodia, and Vietnam. It is a staple herb for Thai classics like pad Thai and the Vietnamese noodle soup known as pho. You can add Thai basil to soups and stir-fried dishes early in the cooking time.