The Northwestern Hawaiian Islands or the Leeward Islands are the small islands and atolls in the Hawaiian island chain located northwest (in some cases, far to the northwest) of the islands of Kaua'i and Ni'ihau. All the Northwestern Hawaiian Islands are uninhabited. They are administered by the U.S. state of Hawai‘i except Midway Atoll, which has temporary residential facilities and is administered by the U.S. Fish and Wildlife Service.

The Northwestern or Leeward Hawaiian Islands include:

• Ka‘ula
• Nihoa
• Necker (Mokumanamana)
• French Frigate Shoals (Mokupāpapa)
• Gardner Pinnacles (Pūhāhonu)
• Maro Reef (Nalukakala)
• Laysan (Kauō)
• Lisianski (Papa‘āpoho)
• Pearl and Hermes Atoll (Holoikauaua)
• Midway (Pihemanu) (temporary residential facilities)
• Kure (Kānemiloha‘i)

The Northwestern Hawaiian Islands were formed over the same volcanic hotspot that formed the Emperor Seamounts and the Windward Hawaiian Islands. As the Pacific Plate moved north and later northwest over the hot spot, volcanic eruptions built up islands. The isolated land masses gradually eroded and subsided, evolving from high islands to atolls (or seamounts north of the Darwin Point).

On June 15, 2006, President George W. Bush issued a public proclamation creating Northwestern Hawaiian Islands National Monument under the Antiquities Act of 1906. The Monument encompasses the islands and surrounding waters, forming the largest marine wildlife reserve in the world. 139,000 square miles of ocean has been set aside for protection, about the size of the U.S. State of California. Previous steps have been taken to protect the same area, including a designation as an 'ecosystem reserve' by President Bill Clinton in 2000. The region has been dubbed "America's Galapagos."

• Hawaiian Islands National Wildlife Refuge