The Emydids are the largest, most diverse family of living turtles, with about 100 species in Europe, Africa, and the Americas. Their use of habitat is equally diverse. A few are terrestrial, living on land, such as box turtles and wood turtles. Most are aquatic, living in ponds, streams, or lakes. However, new scientific techniques have revealed that many aquatic Emydids spend a lot of time on land. Turtles are secretive and well-camouflaged, so it is tough to find them. Recently, scientists began gluing small signal-emitting devices (radiotransmitters) to turtles and then followed them for months or years using an antennae to detect the signals. While it was already known that aquatic turtles nest on land, radio-tracking revealed that they may also hibernate for the winter on land, travel over land to other bodies of water with better food supplies, or even just warm up while buried under leaves in a sunny spot.

The earliest archaeological evidence of humans eating turtles is at a site in northern Spain that is more than one million years old. In historic time, turtles remained popular as food. Huge lakes in the Central Valley of California were trawled by boats, who supplied the markets of San Francisco with thousands of turtles during the early 1900s. Australian aborigines today eat roasted turtle meat, using their shells as serving dishes. Amazonian tribes harvest river turtles for meat and fat. Farm-raised snapping turtles in the southeastern U.S. are the turtle in turtle soup. Asian cuisine particularly favors turtles. Massive turtle farming operations in China churn out soft-shell turtles for consumption, and turtle meat might grace the table at a traditional wedding. Besides their value as food, turtles are exploited heavily for the pet trade, and in Central America their eggs fetch a high price for their supposed aphrodisiac properties.