Chiang Saen is a district (amphoe) in the northern part of Chiang Rai province, northern Thailand. Chiang Saen is an important entrepôt for Thailand's trade with other countries on the upper part of Mekong River.

Chiang Rai is one of Thailand's seventy-six provinces, which lies in upper northern Thailand and is Thailand's northernmost province. It is bordered by the Shan State of Myanmar to the north, Bokeo province of Laos to the east, Phayao to the south, Lampang to the southwest, and Chiang Mai to the west. The provinces is linked to Houayxay Laos by the Fourth Thai–Lao Friendship Bridge that spans the Mekong.