You'll need to get a backcountry use permit if you wish to stay in the Yellowstone wilderness overnight, but these can be obtained for free at most park visitor centers and ranger stations in the 48-hour window before your trip. The National Park Service recommends getting your permit at the facility nearest your destination to get the most up-to-date and accurate information on trail conditions. Obtain your permit from the following locations in Yellowstone: Bechler Ranger Station, Bridge Bay Ranger Station, Grant Village Visitor Center, Canyon Visitor Center, Old Faithful Ranger Station, South Entrance Ranger Station, Tower Backcountry Office and West Yellowstone Visitor Information Center.
You can reserve backcountry campsites in advance, and these approximately 300 overnight spots are spread across the Yellowstone wilderness in any direction you want to go. The NPS accepts applications for overnight stays between January 1 and October 31, as of spring 2013. Those submitted before March 31 are randomly selected for processing, while applications submitted after April 1 are processed in the order they are received. Submit your request in writing to Backcountry Office, P.O. Box 168, Yellowstone National Park, WY ,or call 207-344-2160 for more information. Most campsites are not available for advance reservations, so you can often wait until you arrive in Yellowstone to get your campsite with your permit.
A large population of grizzly bears lives in Yellowstone, and care should be taken to avoid disturbing these aggressive creatures. Avoid carrying food and toiletries with strong scents that could attract bears, and sleep at least 100 yards from the place you cook and where you decide to hang your food. Do not wash yourself or any of your items in Yellowstone's rivers, lakes or ponds. Bury waste at least 6 inches underground and at least 200 feet from campsites or water sources. Bring your own water or boil any you obtain from Yellowstone's water sources to avoid contamination. Remember that Yellowstone's thermal areas should be treated carefully. Don't walk off trails near geysers and other geothermal features -- people have fallen through thin crust and been killed by scalding water.
Each campsite has a set limit for occupancy, which varies by location. Check with rangers before planning to bring a large group. The maximum length of stay also varies, between one and three nights. You can light campfires, but only in the established fire pits at each site. Some of the backcountry campsites do not allow you to burn wood fires, and gathering firewood in the park is not permitted.
