The United States of America (USA), commonly referred to as the United States (U.S.) or America, is a federal republic composed of 50 states, a federal district, five major territories and various possessions. The 48 contiguous states and Washington D.C. are in central North America between Canada and Mexico. The state of Alaska is in the northwestern part of North America and the state of Hawaii is an archipelago in the mid-Pacific. The territories are scattered about the Pacific Ocean and the Caribbean Sea. At 9.8 million square kilometres (3.8 million square miles) and with over 320 million people, the country is the world's third-largest by total area and the third most populous. It is one of the world' most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. Approximately 80% of the population speaks English (the de facto national language) with the combined total of all languages other than English making up the remaining 20%.

The geography and climate of the U.S. are also extremely diverse and the country is home to a wide variety of wildlife. The U.S. arguably has the most diverse fauna in the world and has many distinctive indigenous species found nowhere else on Earth. An estimated 432 species of mammals characterize the fauna of the continental U.S. More than 800 species of bird and there are more than 100,000 known species of insects. There are 311 known reptiles, 295 amphibians and 1,154 known fish species in the U.S. The bald eagle is both the national bird and national animal of the United States and is an enduring symbol of the country itself.

Huge parts of the country with the most distinctive indigenous wildlife are protected as national parks. As of 2013, the U.S. had more than 6,770 national parks or protected areas, all together more than 2,607,131 square kilometres (1,006,619 square miles). Established in 1872 and located in the states of Wyoming and Montana, the first national park was Yellowstone National Park. Home to 67 species of mammals, including the gray wolf, elk, bison and grizzly bear. Yellowstone National Park is widely considered to be the finest large mammal wildlife habitat in the U.S.

Of the total land area of the continental U.S., approximately 7% of it is covered by water including inland (freshwater) and coastal water (saltwater) and the Great Lakes. The mainland U.S. also borders the Pacific, Atlantic and Arctic Oceans, the Gulf of Mexico and the Bering Sea. This represents a large and very diverse habitat for numerous native and introduced game fish species.