Dozens of tiny islands, atolls and shoals, spanning more than 1,200 miles of the world’s largest ocean, are slowly, quietly slipping into the sea, destined to become seamounts. Hundreds of miles north of Kaua‘i, places like Nihoa, Laysan, Pearl and Hermes and Kure comprise the little known, rarely visited Northwestern Hawaiian Islands. The living coral reef colonies of the Northwestern Hawaiian Islands are a spectacular underwater landscape covering thousands of square miles and composing the majority of coral reefs in the United States. These reefs are some of the healthiest and most undisturbed coral reefs on the planet. The Northwestern Hawaiian Islands coral reefs are the foundation of an ecosystem that hosts more than 7,000 species, including marine mammals, fishes, sea turtles, birds, and invertebrates. Many are rare, threatened, or endangered. At least one quarter are endemic, found nowhere else on Earth. Many more remain unidentified or even unknown to science. This Encyclopedia is meant to provide natural history information, video clips, still images, and additional resources to find more information about the marine life found within the Northwestern Hawaiian Islands.