Reservations are very important at some parks, especially during the peak season on May through August. You've got two options to make reservations: internet reservations and telephone.

Internet reservations: http://reservations.nps.gov/index.cfm

Telephone reservations: A central reservation service handles campground and tour reservations at several of the most popular parks. The call center is open 10am to 10pm, Eastern time.

• For Campground Reservations, call 1-800-365-CAMP (2267)
• For reservations at Yosemite National Park, call 1-800-436-PARK (7275)
  
• To book tours, call 1-800-967-CAVE (2283)
  
• For TDD service, call 1-888-530-9796
  
• If you care calling from outside the US or Canada, call 301-722-1257