Entering Tibet requires a travel permit through the Tibet Tourism Bureau. This red tape guarantees travel agents’ their jobs (permit fee Y50, processing fee Y450) and filters out travelers who can’t plan a week in advance. Since the application requires copies of everyone’s passports, it make things much easier to make PDFs of your passport so you can shoot it over to your travel agent of choice (most in the major cities can handle this, not just those in the jump off points of Xining, Xi’an, or Chengdu). In a pinch, you can also take a snapshot of it and convert that to a PDF. We did it this way and will get ours in four days, including express mail delivery to our hotel in Shanghai.