A land bridge is a term in biogeography. It is a narrow land connection between otherwise separate areas, sometimes called an isthmus.

Its significance is that animals and plants may cross over it when the sea level is lower. They cannot easily cross when the sea level is higher, and water covers the land bridge. The separation of a once connected population often leads to speciation, the splitting of one species into two and the two species change over time to be different but have distant similarities.