Car campers shouldn't have any problem finding a place to pitch a tent or park an RV, especially in the northern half of the state. The White Mountain National Forest maintains 20 campgrounds with a total of 819 sites (no hookups), some very small and personal, others quite large and noisy. Sites tend to be fairly easy to come by midweek, but on summer or foliage weekends, you're taking a chance if you arrive without reservations.
For National Forest Campground reservations, call the National Recreation Reservation Service (tel. 877/444-6777). Reservations may also be made at www.reserveusa.com, a useful and sophisticated site that enables you to read up on individual campsites (including distance to the nearest water faucet and suitability for RVs or those with disabilities) and reserve the campsite you want online.
For advance reservations at one of the state parks in or around the White Mountains, call tel. 603/271-3628 between January and May; during the summer season, call the campground directly or, better yet, reserve online at www.nhstateparks.org. Some campgrounds are first-come, first-served. A list of parks and phone numbers is listed in the New Hampshire Visitor's Guide, available at information centers, or from the Division of Travel and Tourism Development, P.O. Box 1856, Concord, NH 03302 (tel. 800/386-4664; www.visitnh.gov).