The Bering land bridge was a land bridge roughly 1,000 miles (1,600 km) wide (north to south) at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages. The term Beringia was first coined by the Swedish botanist Eric Hultén in 1937. Like most of Siberia and all of Manchuria, Beringia was not glaciated because snowfall was extremely light. The grassland steppe, including the land bridge, that stretched for several hundred miles into the continents on either side has been called Beringia. It is believed that a small human population of at most a few thousand survived the Last Glacial Maximum in Beringia, isolated from its ancestor populations in Asia for at least 5,000 years, before expanding to populate the Americas sometime after 16,500 years ago, during the Late Glacial Maximum as the American glaciers blocking the way southward melted.

The Bering Strait, the Chukchi Sea to the north and the Bering Sea to the south, are all shallow seas (see maps). During cycles of global cooling, such as the most recent ice age, enough sea water became concentrated in the great ice sheets that covered North America and Europe, so that the subsequent drop in eustatic sea levels exposed shallow sea-floors that have subsequently re-flooded. Other land bridges around the world have emerged and disappeared in the same way. Approximately 14,000 years ago, mainland Australia was linked to both New Guinea and Tasmania; the British Isles formed an extension of continental Europe via the dry beds of the English Channel and North Sea; and the dry basin of the South China Sea linked Sumatra, Java and Borneo to the Asian mainland.

A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonise new lands. Land bridges can be created by marine regression, in which sea levels fall, exposing shallow, previously submerged sections of continental shelf; or when new land is created by plate tectonics; or occasionally when the sea floor rises due to post-glacial rebound after an ice age.

In the 19th century a number of scientists noted puzzling geological and zoological similarities between widely separated areas. To solve these problems, "…whenever geologists and paleontologists were at a loss to explain the obvious transoceanic similarities of life that they deduced from the fossil records, they sharpened their pencils and sketched land bridges between appropriate continents." The concept was first proposed by Jules Marcou in Lettres sur les roches du Jura.

These hypothetical land bridges included:

All of these became obsolete with the gradual acceptance of continental drift and the development of plate tectonics by the mid-20th century.