Martin Litton (born February 13, 1917) is a legendary Grand Canyon river runner and a longtime environmental activist, best known as a staunch opponent of the construction of Glen Canyon Dam and other dams on the Colorado River.

Although not a well-known environmental activist until the 1950s, as early as October 1935 he wrote a letter to the Los Angeles Times at the age of 18, which read in part: "The people of the entire state should rise up against the destruction of Mono Lake. Mono Lake is a gem-among California's greatest scenic attractions."

He first floated the Colorado River through the Grand Canyon in 1955, at the time becoming only the 185th person known to have made the trip down the river first pioneered by John Wesley Powell. He ran the river again in 1962 and continued to run the Colorado for decades afterward, founding Grand Canyon Dories in 1971 and running commercial river trips through the 1970s and 1980s. Litton showed a contrarian preference for using small wooden boats, known as dories, at a time when other river runners had mostly switched to inflatable rubber rafts. These boats were originally used in Oregon; it was Litton who adapted their use to the Colorado River. He sold the business in 1990.

Litton was a close friend of David Brower, Edward Abbey, and other major figures in the conservation movement. Brower first recruited him in 1952 for a campaign to oppose the construction of two dams in Dinosaur National Monument. Congress voted down approval for the dams in 1956. This began a longtime association with the Sierra Club and a lifelong opposition to dam-building on the Colorado. He was active in the fight to stop dams from being constructed within Grand Canyon National Park. A 1964 river trip led by Martin Litton, which included David Brower and Francois Leydet, led to the publication of the 1964 book authored by Leydet, Time and the River Flowing, which helped galvanize opposition to the proposed dams within the Grand Canyon.

Between 1954 and 1968 he was the travel editor for Sunset Magazine. In 1960, Sunset ran a cover story entitled "The Redwood Country," which is credited with launching a campaign which eventually led to the establishment of Redwood National Park.

Litton is the author of the 1968 book The Life and Death of Lake Mead. He has been featured in documentary films including Monumental: David Brower's Fight for Wild America and River Runners of the Grand Canyon.

He has remained active in environmental causes. His most recent environmental activities have revolved around opposing logging in the Sequoia National Forest and the recently created Giant Sequoia National Monument, and campaigning to remove Glen Canyon Dam and drain Lake Powell.

He still continues to make occasional river trips. In 1999 at the age of 82, he broke his own record as the oldest person to run the Grand Canyon, rowing the entire trip in a wooden boat.

Litton served on the Board of Directors of the Sierra Club from 1964 to 1973. He currently serves on the Advisory Committee of the Southern Utah Wilderness Alliance and on the Honorary Board of Directors of the Glen Canyon Institute. In 2005, he was a write-in candidate for the Sierra Club Board of Directors, but did not win election.