[15] The oldest text of term Muay ever recorded, found in the palm-leaf manuscripts in Northern Thai language called Mungrai Law 1839 BE, enacted 1296 AD.

The Mungrai Customary Law 1296 CE (Mungraiyashastra), one of the oldest palm-leaf manuscripts written in the Northern Thai language during the reign of King Mangrai, who established the town of Chiang Mai (1292–1311),[16]: 31  also mentioned the Tai martial arts (Muay) in section 7, under the article of 18 types of quarrels,[21] for the first time in the Lan Na Kingdom.

In the folklore, the Legend of the Phayao Kingdom (1094–1338), the version by Wat Sriboonrueng mentioned the Tai martial arts (Muay) known as jerng tiw khui[22] during the reign of King Chueang Maharat (1115–1162).

He taught a variety of subjects, collectively known as Maiya Shastra (ಮೈಶಾಸ್ತ್ರ), which included martial arts (Muay), sword fighting, archery, and elephant and horse control.

[16]: 40  Later, King Maha Thammaracha I was trained in essential subjects as well as practical skills, including martial arts (Muay) for self-defense with bare hands and the use of weapons.

Muay Thai was also taught at temples, which served as learning centers for the Tai peoples, following the guidelines of King Ram Khamhaeng's war strategy manual.

[27] The inscription of Khun Sri Chaiya Raj Mongkol Thep (N.M. 78, Face 2) 1431 AD reads: King Borommarachathirat II of Ayutthaya commanded his warrior, Khun Sri Chaiya Raj Mongkol Thep, to march four military forces to assault Angkor Thom, Phimai, and Phanom Rung to become states under his endless mandate.

The King then assigned Khun Sri Chaiya Raj Mongkol Thep, groups of Siamese boxers (Muay), and military forces with elephants and horse battalions to the retreat procession to the Kingdom of Ayutthaya.

[38] Monsieur Braud's letter to Directors of the International Affairs Kingdom of Ayutthaya (June 9, 1699) reads: This news caused vassals of the Siamese Royal Court to be suddenly shocked.

The government official responded to the king that the temple fair will be held at Khwaeng Wiset Chai Chan[39]: 283  (now Ang Thong province, Thailand).

[39]: 283 On the next festival day, King Suriyenthrathibodi disguised himself as the general public with a few royal police and went to the festival by boat to join the Muay boxing competitions, and he won both the first and second matches during the competition, as the Royal Chronicle of the Kingdom of Ayutthaya reads: King Suriyenthrathibodi requested the second match; the boxing referee then rearranged another rival to compete with him.

The King then stated a royal order to arrange for a Siamese man named Nai Khanom Tom, a famous fighter from Ayutthaya, to confront a Burmese boxer in front of the throne.

[42] This historiography was largely extrapolated from brief mentions in written records, including four episodes in the royal chronicles of the 18th century: one where King Sanphet VIII fought an incognito match at a temple fair, Khwaeng Mueang Wiset Chai Chan in 1702;[39]: 283  one where Nai Khanom Tom,[39]: 414  as a war captive following the fall of Ayutthaya, fought in front of the Burmese king and defeated ten Burmese fighters; one of the military commander Phraya Phichai Dap Hak, who in his youth was a Muay Thai fighter; and one of Muen Phlan, who was chosen by King Rama I to fight against two French challengers in 1788.

[46][47]King Rama I accepted his brother's advice and asked a nobleman to inform the Frenchmen that a match would be arranged with a purse of fifty Chang (equivalent to 4,000 baht at the time).

[44][46] On the day of the boxing competition, King Rama I, his younger brother, and many members of the Siamese royal court were present as spectators near the western theater of Wat Phra Kaew.

Prince Maha Sura Singhanat arranged for a Siamese boxer from the Front Palace King's Guard Department named Muean Phlan[46] to compete against the younger of the French brothers.

As a result, an amendment was made in the IFMA constitution to change the name of the sport from "Muay Thai" to "Muaythai" – written as one word in accordance with Olympic requirements.

[59] According to IFMA rules, Muay Thai is a full contact martial art that uses the fists, elbows, knees and feet to strike an opponent.

Strikes to the groin were allowed in Muay Thai boxing until the late 1980s, and are still permitted in Thailand itself, and in club or competition events that abide to the traditional rules.

Young men would tear off pieces of a loved one's clothing (often a mother's sarong) and wear it in battle for good luck as well as to ward off harmful spirits.

The punch techniques in Muay Thai were originally quite limited, being crosses and a long (or lazy) circular strike made with a straight (but not locked) arm and landing with the heel of the palm.

Hooks are often blocked with a motion sometimes described as "combing the hair", that is, raising the elbow forward and effectively shielding the head with the forearm, flexed biceps and shoulder.

In 2016, 9,998 children under the age of 15 were registered with Board of Boxing under the Sport Authority of Thailand, according to the Child Safety Promotion and Injury Prevention Research Centre (CSIP).

[68] The Advanced Diagnostic Imaging Centre (AIMC) at Ramathibodi Hospital studied 300 child boxers aged under 15 with two to more than five years of experience, as well as 200 children who do not box.

"[67] At the 13th World Conference on Injury Prevention and Safety Promotion in 2018, it was revealed that up to three percent of the upcoming generation will grow up with learning disabilities unless an amendment is ratified that bans children under 12 from participating in boxing matches.

[74] An infamous alleged case of match-fixing was the bout on 12 October 2014 in Pattaya between top Thai boxer Buakaw Banchamek and his challenger, Enriko Kehl, at the K-1 World Max Final event.

[75] This can create a steep learning curve for newcomers to muay Thai but allows for rapid increases in fitness and stamina provided one avoids overtraining.

As such, practitioners will repeatedly hit a dense heavy bag with their shins, conditioning it, hardening the bone through a process called cortical remodelling.

The trainer will often also wear a belly pad around the abdominal area so that the fighter can attack with straight kicks or knees to the body at any time during the round.

Specific tactics and strategies can be trained with sparring including in close fighting, clinching and kneeing only, cutting off the ring, or using reach and distance to keep an aggressive fighter away.