The Continental Divide Trail is the third and longest of the Triple Crown of Hiking, at just around 3100 miles in length. On the north end, the trail starts in Glacier National Park, right at the Canadian Border. It then winds south through Montana, Idaho, Wyoming, Colorado, and New Mexico. The southern terminus is close to the town of Antelope Wells in New Mexico. It roughly follows the Continental Divide.
The CDT is quite possibly the most remote of the three big trails with long stretches without towns or other signs of civilization. Along the way, it passes through some of the most amazing and scenic land in the country including Glacier National Park, Yellowstone National Park, Rocky Mountain National Park, and many established wilderness areas. Most of the land for the trail is currently held by federal agencies though large chunks remain privately held, so the trail is not yet complete. Hikers should be advised that they will be wandering across private lands without trail markers.
The CDT was proposed in 1966 by Benton Mackaye, the same man who founded the Appalachian Trail. Under the National Trails System Act, Congress gave the go-ahead for the study of such a trail along the Continental Divide. The study found there'd be great interest in such a trail because of the isolation, historic interest, and scenic beauty. So, construction on the trail began in 1978. The first step in construction was identifying existing trails and roads (logging roads or fire roads) which could be incorporated into the trail to cut down costs. However, no money was allocated to finish the trail so much of the money comes through fundraising efforts. Management of the trail is split between the Forest Service, the National Park Service, and the Bureau of Land Management.
This information based upon a reading of the Continental Divide Trail Alliance website, http://www.cdtrail.org.