The Ramakien (Thai: รามเกียรติ์, RTGS: Rammakian, pronounced [rāːm.mā.kīa̯n]; lit. 'Glory of Rama'; sometimes also spelled Ramakian) is one of Thailand's national epics. It is a Thai version of the ancient Indian Hindu epic Ramayana, and an important part of the Thai literary canon.

King Rama VI was the first person to shed light first on the Ramayana studies in Thailand, by tracing the sources of the Ramakien, comparing it with the Sanskrit Valmiki Ramayana. He found that the Ramakien was influenced by three sources: the Valmiki's Ramayana, the Vishnu Purana, and Hanuman Nataka. A number of versions of the epic were lost in the destruction of Ayutthaya in 1767. Three versions currently exist, one of which was prepared in 1797 under the supervision of (and partly written by) King Rama I. His son, Rama II, rewrote some parts of his father's version for khon drama. The work has had an important influence on Thai literature, art and drama (both the khon and nang dramas being derived from it).

While the main story is similar to that of the Dasaratha Jataka, differences in some tales still prevail. Many other aspects were transposed into a Thai context, such as the clothes, weapons, topography, and elements of nature, which are described as being Thai in style. As Thailand is considered a Theravada Buddhist society, the Buddhist history latent in the Ramakien serves to provide Thai legends with a creation myth, as well as representations of various spirits which complement beliefs derived from Thai animism.

A painted representation of the Ramakien is displayed at Bangkok's Temple of Emerald Buddha, and many of the statues there depict characters from it.

The Ramayana came to Southeast Asia by means of Buddhist missionaries, Indian traders, and scholars who traded with Khmer kingdoms (such as Funan and Angkor) and Srivijaya, with whom the Indians shared close economic and cultural ties. The Thai adopted from the Khmer people components of Indianized culture such as the Ramayana.

In the late first millennium, the Ramakien epic (written as Ramkerti, รามเกียรติ์ but read as Ramakien) was adopted by the Thai people. The oldest recordings of the early Sukhothai kingdom, dating from the 13th century, include stories from the Jataka legends. The history of the legends was told in the shade theater (Thai: หนัง, Nang), a shadow-puppet show in a style adopted from Indonesia, in which the characters were portrayed by leather dolls manipulated to cast shadows on a nearby screen as the audience watched from the other side.

The Thai version was first written down in the 18th century, during the Ayutthaya Kingdom, following the demise of the Sukhothai government. Most editions, however, were lost when the city of Ayutthaya was destroyed by armies from Burma (modern Myanmar) in the year 1767.

The version recognized today was compiled in the Kingdom of Siam under the supervision of King Rama I (1726–1809), the founder of the Chakri dynasty, which still maintains the throne of Thailand. Between the years of 1799 and 1807, Rama I supervised this well-known recension and even wrote parts of it. It was also under his reign that construction began on the Thai Grand Palace in Bangkok, which includes the grounds of the Wat Phra Kaew, enshrining the Emerald Buddha. The walls of the Wat Phra Kaew are lavishly decorated with paintings representing parts of the Ramakien.