All PCT thru-hikers will need to get a Thru-Permit. Anyone planning on entering Canada via the PCT will also need a permit to enter Canada. Finally, if you plan on making camp fires or using a camp stove in California then you will need a California Campfire Permit.
Permits are required in all National Parks, wilderness areas, and other restricted areas along the PCT. The good news is, if you plan on hiking 500 continuous miles (or more), the PCTA can issue you a Thru-Permit for free (however we recommend sending them a $10 donation). Your Thru-Permit will give you unfettered access to all the National Parks, wilderness areas, and other restricted areas along the PCT. The Thru-Permit also gives you permission to camp along the PCT.
The Thru-Permit does NOT allow you to stay at pay-camp-sites for free, and does not function as a trailhead parking pass. Permission to climb Mt. Whitney costs an additional $15.
Make sure you get your Thru-Permit several weeks before the start of your trip. Application processing begins January 31st of each year. Fill out the Thru-Permit Application Form and follow the instructions therein.
Entering Canada along the Pacific Crest Trail requires a permit. Though the permit is free, the Canadian Government can be very strict in deciding who may and may not enter their country. Any criminal history (ie: a DUI) may result in you being denied a permit. If you don't think Canada will open her doors to you, but you really, really, want to get in anyway, then you'll need to be deemed reabilitated.
Between two and three months before leaving on your trip, fill out The Application for Entry to Canada via Pacific Crest Trail. Follow the instructions on the form.
You can read more about the rules and regulations around entering Canada by clicking here.
Finally, the Canadian Government wants to you have some sort of I.D. (a driver's license will work just fine) BUT Americans are required to have a U.S. Passport to get back into the United States. You can get back in without one, but it's quite a hassle and may take several hours.
The California Campfire Permit is free and allows you to make campfires and use stoves in all Park Service, Forest Service, BLM and State Lands within the State of California (Oregon and Washington don't require one). California just wants to make sure you know the rules and regulations about fire in the backcountry.
Permits are valid for one year. Make sure to have your permit sent before you start your trip. Call the Forest Service Regional Office at 707-562-8794 and request a campfire permit to be mailed to you. Permits can also be picked up at any US forest service, National Park service, BLM, or California Division of Forestry office.