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 body temperature of a turtle changes with the temperature of its environment, making cold-blooded a misnomer. The blood temperature of a turtle sitting on a rock in full sunshine may be quite warm. Its dependence on outside temperatures, or ectothermy (ecto= outside; thermy= temperature) compels turtles to seek places with desirable temperatures. Every turtle species has a preferred temperature range for digestion and other metabolic processes. To get within range, some turtles need to sit in the sun (bask) for at least part of the day. Basking also dries out a turtle's shell, which might inhibit growth of algae or drive away other parasites that need moisture. A typical pattern is to bask in the morning until its body temperature gets high enough for a turtle to be active. Time spent seeking food (foraging) competes with basking. A turtle often alternates basking with foraging during the daylight hours.