Dhammayut literally means "In Accordance with the Dhamma". This sect based on the Pali canon and begun in the 1820's by Prince Mongkut at the time was Reform Buddhism. Institutionally this movement changed Buddhism from a wat-localized to a Sangha-centred religion. Lay religiosity is moving the same way.

Prince Mongkut studied the canon during his early years as a monk. He grew discouraged by the level of practice he saw around him in Thai monasteries, and later re-ordained from the Mons, an ethnic group that straddled the Thai-Burmese border, where he studied Vinaya and the classic dhutanga practices under the guidance of a Mon teacher. Later, his brother, King Rama III, complained that it was disgraceful for member of the royal family to join an ethnic minority, and so built a monastery for the Prince-Monk on the Bangkok side of the river. There, Mongkut attracted a small but strong following of like-minded monks and lay supporters, and in this way the Dhammayut movement was born. After twenty-seven years of monk life, prince Mongkut ascended the throne and became King Rama IV (portrayed in the musical The King and I) after his brother's death in 1851. Rama IV later sponsored the building of new Dhammayut centers in the capital and the provinces, which was how -- by the time of Ajaan Mun -- there came to be a handful of Dhammayut monasteries in Ubon.

In its early years, the Dhammayut movement was an informal grouping devoted to Pali studies, focusing on Vinaya, the classic dhutanga practices, a rationalist interpretation of the Dhamma, and the revival of meditation techniques taught in the Pali canon, such as recollection of the Buddha and mindfulness of the body. But in reality Bangkok encouraged Pali scholarship but ignored meditation.

Mongkut and the movement's members could not prove the teachings of the Pali canon actually led to enlightenment but believed a great deal of merit could revive the earliest Buddhist traditions. Therefore Mongkut and many of his students took a bodhisattva vow and dedicated the merit of his efforts to future Buddhahood.

In terms of Sangha system, the Reform Buddhism movement pulled monks toward the center (Bangkok) by rewards while regulations reached out into the countryside. Rewards such as title, honor, position, and gift encouraged reform and allowed the Sangha government to control monks and wat. Administrative monks owned titles and encouraged by well kept temples and so wat prospered physically.