The Royal Thai Armed Forces (RTARF) (Thai: ; RTGS: Kong Thap Thai) are the armed forces of the Kingdom of Thailand.

The nominal head of the Thai Armed Forces (; RTGS: Chom Thap Thai) is the King of Thailand. The armed forces are managed by the Ministry of Defense of Thailand, which is headed by the minister of defence and commanded by the Royal Thai Armed Forces Headquarters, which in turn is headed by the Chief of Defence Forces. The commander in chief of the Royal Thai Army is considered the most powerful position in the Thai Armed Forces.Royal Thai Armed Forces Day is celebrated on 18 January to commemorate the victory of King Naresuan the Great in battle against the Crown Prince of Burma in 1593.

King Naresuan the Great ((Thai: สมเด็จพระนเรศวรมหาราช, RTGS: Somdet Phra Naresuan Maharat, pronounced [sǒmdèt pʰráʔ nārēːsǔa̯n māhǎːrâːt] listen ) or Sanphet II (Thai: สรรเพชญ์ที่ ๒), (Burmese: နရဲစွမ် (သို့) ဗြနရာဇ်); 1555/1556 – 25 April 1605) was the 18th monarch of Ayutthaya Kingdom and 2nd monarch of the Sukhothai dynasty. He was the king of the Ayutthaya Kingdom from 1590 and overlord of Lan Na from 1602 until his death in 1605. Naresuan is one of Thailand's most revered monarchs as he is known for his campaigns to free Ayutthaya from the vassalage of the Taungoo Empire. During his reign, numerous wars were fought against Taungoo Burma. Naresuan also welcomed the Dutch.: 242