Thai cuisine (Thai: อาหารไทย, RTGS: ahan thai, pronounced [ʔāː.hǎːn tʰāj]) is the national cuisine of Thailand.

Thai cooking places emphasis on lightly prepared dishes with aromatics and spicy heat. The Australian chef David Thompson, an expert on Thai food, observes that unlike many other cuisines, Thai cooking is "about the juggling of disparate elements to create a harmonious finish. Like a complex musical chord it's got to have a smooth surface but it doesn't matter what's happening underneath. Simplicity isn't the dictum here, at all."

Traditional Thai cuisine loosely falls into four categories: tom (Thai: ต้ม, boiled dishes), yam (Thai: ยำ, spicy salads), tam (Thai: ตำ, pounded foods), and kaeng (Thai: แกง, curries). Deep-frying, stir-frying and steaming are methods introduced from Chinese cuisine.

In 2011, seven Thai dishes appeared on a list of the "World's 50 Best Foods", an online poll of 35,000 people worldwide by CNN Travel. Thailand had more dishes on the list than any other country: tom yum kung (4th), pad thai (5th), som tam (6th), massaman curry (10th), green curry (19th), Thai fried rice (24th) and nam tok mu (36th).

Thai cuisine and the culinary traditions and cuisines of Thailand's neighbors, especially Cambodia, Laos, Myanmar, India, Malaysia and Indonesia, have influenced one another over the course of many centuries.

According to the Thai monk Venerable Buddhadasa Bhikku's writing, ‘India's Benevolence to Thailand’, Thai cuisine was influenced by Indian cuisine. He wrote that Thai people learned how to use spices in their food in various ways from Indians. Thais also obtained the methods of making herbal medicines from the Indians. Some plants like sarabhi of the family Guttiferae, panika or harsinghar, phikun or Mimusops elengi and bunnak or the rose chestnut etc. were brought from India. According to the book Mae Khrua Hua Pa (first published in 1908) by Lady Plian Bhaskarawongse, she found that Thai cuisine had a strong gastronomical cultural line from Sukhothai (1238–1448) through Ayuttthaya (1351–1767) and Thonburi period (1767–1782) vis-à-vis Siamese governmental officers' daily routines (such as royal cooking) and their related cousins. Thai food during the Thonburi period tended to be more similar to that from the Ayutthaya period, except the addition of Chinese food resulted from her prosperous international trade.

Western influences, starting in 1511 when the first diplomatic mission from the Portuguese arrived at the court of Ayutthaya, have created dishes such as foi thong, the Thai adaptation of the Portuguese fios de ovos, and sangkhaya, where coconut milk replaces cow's milk in making a custard. These dishes were said to have been brought to Thailand in the 17th century by Maria Guyomar de Pinha, a woman of mixed Japanese-Portuguese-Bengali ancestry who was born in Ayutthaya, and became the wife of Constantine Phaulkon, a Greek adviser to King Narai. The most notable influence from the West must be the introduction of the chili pepper from the Americas in the 16th or 17th century. It, and rice, are now two of the most important ingredients in Thai cuisine. During the Columbian Exchange, Portuguese and Spanish ships brought new foodstuffs from the Americas including tomatoes, corn, papaya, pea eggplants, pineapple, pumpkins, culantro, cashews, and peanuts.

Regional variations tend to correlate to neighboring states (often sharing the same cultural background and ethnicity on both sides of the border) as well as climate and geography. Northern Thai cuisine shares dishes with Shan State in Burma, northern Laos, and also with Yunnan Province in China, whereas the cuisine of Isan (northeastern Thailand) is similar to that of Southern Laos, and by Vietnamese cuisine to its east. Southern Thailand, with many dishes that contain liberal amounts of coconut milk and fresh turmeric, has that in common with Indian, Malaysian, and Indonesian cuisine.