The United States has ten protected areas known as national seashores and four known as national lakeshores, which are operated by the National Park Service, an agency of the Department of the Interior. National seashores and lakeshores must be established by an act of the United States Congress. National seashores and lakeshores are coastal areas federally designated as being of natural and recreational significance as a preserved area. The first national seashore, Cape Hatteras, was established in 1953, and Indiana Dune National Lakeshore was established in 1966. The newest national lakeshore or seashore is Canaveral, established in 1975. All of the national lakeshores are on Lakes Michigan and Superior, and nine of the ten national seashores are on the Atlantic Ocean, including two on the Gulf of Mexico.

National seashores are located in ten states and national lakeshores are in four other states. Florida, North Carolina, and Michigan each have two. The largest national seashore or lakeshore is Gulf Islands, at over 137,000 acres (550 km²); the smallest is Indiana Dunes, at 15,000 acres (61 km²). The total areas protected by national seashores and lakeshores are approximately 595,000 acres (2,410 km²) and 229,000 acres (930 km²), respectively.

The Gulf Islands are the islands in the Strait of Georgia (also known as Salish Sea or the Gulf of Georgia, explained in detail below), between Vancouver Island and the mainland of British Columbia, Canada.

According to BC Geographical Names (BCGNIS) the name "Gulf Islands" was originally intended and commonly understood to refer to the archipelago at the southern end of the Strait of Georgia—from Gabriola Island in the north to Saturna Island in the southeast and D'Arcy Island in the southwest. During the 1990s, however, the name began to be applied to all the islands in the Strait of Georgia, resulting in the introduction of the term "Southern Gulf Islands", which BCGNIS calls a misnomer, to distinguish the original "Gulf Islands" from the rest, which are sometimes called the "Northern Gulf Islands". BCGNIS further notes that Quadra Island is increasingly described as the "northermost of the Gulf Islands".

The division of the Gulf Islands into two groups, the Southern and Northern Gulf Islands, is relatively common. The dividing line is approximately that formed by the city of Nanaimo on Vancouver Island, and the mouth of the Fraser River on the mainland. The larger populated islands are served by BC Ferries, which operates combined vehicle and passenger ferries between the Gulf Islands and to terminals near the major cities of Nanaimo and Victoria on Vancouver Island as well as Vancouver on the mainland. BC Ferries distinguishes between the Southern Gulf Islands and the Northern Gulf Islands. Their Northern Gulf Islands includes both Quadra Island and Cortes Island, as well as some islands far to the north, such as Malcolm Island and Cormorant Island.Natural Resources Canada maps the Gulf Islands as including the "Southern Gulf Islands", the islands of Howe Sound (such as Bowen Island, Gambier Island, and Keats Island), along with Lasqueti Island, Hornby Island, and Denman Island.