Ratchadamnoen Avenue (Thai: ถนนราชดำเนิน, pronounced [râːt.tɕʰa.dām.nɤ̄ːn], also spelled Rajdamnern) is a historic road in the Phra Nakhon and Dusit Districts of Bangkok, Thailand.
Ratchadamnoen Avenue was commissioned by King Chulalongkorn following his first visit to Europe in 1897. Construction took place from 1899 to 1903. The road consists of three segments, named Ratchadamnoen Nai, Ratchadamnoen Klang, and Ratchadamnoen Nok (Inner, Middle, and Outer Ratchadamnoen, respectively). It links the Grand Palace to Dusit Palace in the new royal district, terminating at the Royal Plaza in front of the Ananta Samakhom Throne Hall. Inspired by the Champs-Élysées and other European boulevards, the King used the road as a route for grand royal parades (Ratchadamnoen literally means "royal procession"), which served to project images of a modern monarchy.
Ratchadamnoen Nai Road begins at the northeast corner of the Grand Palace and leads northward to the Phan Phiphop Lila Bridge, which crosses the old city moat. The road then continues east as Ratchadamnoen Klang until it crosses Khlong Rop Krung (the outer moat) at Phan Fa Lilat Bridge, where it turns northward toward the Royal Plaza. Ratchadamnoen Nok, in particular, was designed to impart Western-style grandeur, with three carriageways with wide pavements lined by multiple rows of trees.
Today, the avenue serves as a major thoroughfare bringing traffic into the old city centre and across Phra Pin-klao Bridge to the Thonburi side of the city. It is bordered by government offices including Government House. Democracy Monument sits in the centre of Ratchadamnoen Klang Road. The avenue has been the site of many demonstrations, including the 1973 student uprising as well as more recent political rallies.