Free wilderness permits are required year-round for all overnight trips into Yosemite's wilderness. They are not required for day hikes. Yosemite uses a trailhead quota system which limits the number of people who may begin overnight hikes from each trailhead, each day.
This system is designed to avoid overcrowding and to reduce impacts to wilderness areas. At least 40% of each trailhead quota is available on a first come first served basis the day of, or one day prior to, the beginning of your trip.
If you are starting a trip outside the park, obtain a permit from the land agency who manages your entry trailhead. Please plan your trip before you apply for a wilderness permit or write for a reservation.
Permits are also available by advance reservation. Wilderness permits are not a registration; leave an accurate itinerary with family or friends before you begin your trip.