At Glacier backcountry permits are mandatory. There's a limited number of permits and they're doled out on a first-come, first-serve basis, so the best way to ensure you get a pass is to make an advance reservation. You can print out an application online (www.nps.gov/glac/planyourvisit/backcountry.htm); the reservation costs $30. Mail a request and a check after mid-April to Backcountry Reservations, Glacier National Park Headquarters, Box 395, West Glacier, MT 59936 or fax it in with a credit card number (406/888-5819). Once you get to the park you'll then need to stop by the Apgar Backcountry Permit Center to pick up your permit, paying an additional $5 per day. If you don't make an advance reservation, you can stop by the Apgar center after mid-April to request a $5 permit for the following day. This is a long shot, though, as permits often run out.