The Kitsap Peninsula () lies west of Seattle across Puget Sound, in Washington state in the Pacific Northwest. Hood Canal separates the peninsula from the Olympic Peninsula on its west side. The peninsula, a.k.a. "Kitsap", encompasses all of Kitsap County except Bainbridge and Blake Islands, as well as the northeastern part of Mason County and the northwestern part of Pierce County. The highest point on the Kitsap Peninsula is Gold Mountain. The U.S. Navy's Puget Sound Naval Shipyard, and Naval Base Kitsap (comprising the former NSB Bangor and NS Bremerton) are on the peninsula. Its main city is Bremerton.
Though earlier referred to as the Great Peninsula or Indian Peninsula, with "Great Peninsula" still its official name, its current name comes from Kitsap County, which occupies most of the peninsula. It is thus the namesake of Chief Kitsap, an 18th- and 19th-century warrior and medicine man of the Suquamish Tribe. The Suquamish were one of the historical fishing tribes belonging to the Coast Salish group of peoples, and their ancestral grounds were based on the eastern shores of the Kitsap Peninsula. Seattle is named after the tribe's most famous leader, Chief Seattle. The Port Madison Indian Reservation, located between Poulsbo and Agate Pass, is the modern Suquamish tribal center. The Kitsap Peninsula is also home to the Port Gamble S'Klallam Tribe, another branch of the Coast Salish people, whose tribal center is the Port Gamble S'Klallam Indian Reservation at Little Boston located on the northwest coast of the peninsula. And though their main center now is at Skokomish the Hood Canal was the main demesne of the communities of the Twana, another subgroup of the Coast Salish.
The peninsula is connected to the eastern shore of Puget Sound by Washington State Ferries, which run from Bremerton to Downtown Seattle, from Kingston to Edmonds and from Southworth to West Seattle via Vashon Island, by the Tacoma Narrows Bridge from Point Fosdick to Tacoma, and to the northeastern shore of the main Olympic Peninsula by the Hood Canal Bridge.