Sukhothai Historical Park (Thai: อุทยานประวัติศาสตร์สุโขทัย (Pronunciation)) covers the ruins of Sukhothai, literally 'dawn of happiness', capital of the Sukhothai Kingdom in the 13th and 14th centuries, in north central Thailand. It is near the city of Sukhothai Thani, capital of Sukhothai province.

The city's walls form a rectangle about 2 km (1.2 mi) east-west by 1.6 km (0.99 mi) north-south. There are 193 ruins on 70 km² (27 sq mi) of land. There is a gate in the centre of each wall. Inside are the remains of the royal palace and twenty-six temples, the largest being Wat Mahathat. The park is maintained by the Fine Arts Department of Thailand with help from UNESCO, which has declared it a World Heritage Site. Each year, the park welcomes thousands of visitors.

Originally, Sukhothai was a Khmer empire's outpost named Sukhodaya. During the reign of Khmer Empire, the Khmers built some monuments there, several of them survived in Sukhothai Historical Park such as the Ta Pha Daeng shrine, Wat Phra Phai Luang, and Wat Sisawai. About some 50 kilometer north of Sukhothai is another Khmer military outpost of Si Satchanalai or Sri Sajanalaya.

In the mid-13th century, the Tai tribes led by Si Indradit rebelled against the Khmer governor at Sukhodaya and established Sukhothai as an independent Tai state and remained the center of Tai power until the end of the fourteenth century.

Prior to the 13th century, a succession of Tai kingdoms existed in the northern highlands including the Ngoenyang (centered on Chiang Saen, predecessor of Lan Na) kingdom and the Heokam (centered on Chiang Hung, modern Jinghong in China) kingdom of Tai Lue people. Sukhothai had been a trade center and part of Lawo, which was under the domination of the Khmer Empire. The migration of Tai people into the upper Chao Phraya valley was somewhat gradual.

Modern historians believe that the secession of Sukhothai (once known as Sukhodaya) from the Khmer empire began as early as 1180 during the reign of Pho Khun Sri Naw Namthom who was the ruler of Sukhothai and the peripheral city of Sri Satchanalai (modern day Si Satchanalai District in Sukhothai Province). Sukhothai had enjoyed substantial autonomy until it was re-conquered around 1180 by the Mons of Lawo under Khomsabad Khlonlampong.

Two brothers, Pho Khun Bangklanghao and Pho Khun Phameung took Sukhothai from Mon hands in 1239. Khun (ขุน) before becoming a Thai feudal title, was a Tai title for a ruler of a fortified town and its surrounding villages, together called a muang; in older usage prefixed pho (พ่อ) 'father', Comparable in sound and meaning to rural English 'paw'. Bangklanghao ruled Sukhothai as Sri Indraditya and began the Phra Ruang dynasty. He expanded his kingdom to bordering cities. At the end of his reign in 1257, the Sukhothai Kingdom covered the entire upper valley of the Chao Phraya River (then known simply as Menam, 'mother of waters', the generic Thai name for rivers.)

Traditional Thai historians considered the founding of the Sukhothai Kingdom as the beginning of the Thai nation because little was known about the kingdoms prior to Sukhothai. Modern historical studies demonstrate that Thai history began before Sukhothai. Yet the foundation of Sukhothai is still a celebrated event.