The tortoise is a reptile that lives exclusively on land. The name "tortoise" actually refers to the taxonomic family testudinidae, and there are therefore a wide variety of tortoises of different species. Tortoises can be found throughout the world.

The tortoise is perhaps best known for its shell. However, it is less well known that this shell actually consists of two layers. The outer layer of the shell is hard and made of scales, and conceals the inner layer, which is made of bone. Most tortoise's vertebrae are fused to their shells The shell consists of a top portion that covers the turtle's back, and a lower portion that covers its underside. These segments of the shell are joined by a bridge at the tortoise's side.

If the tortoise is not known best for its shell, it is known best for its speed, or lack thereof. Giant tortoises move particularly slowly, with an average speed of less than .2 miles per hour. The fastest speed at which a tortoise has been recorded moving is five miles per hour.

Tortoises use their shells as protection by withdrawing their heads into them when they detect a threat. Their eyes are also protected by heavy lids. Because of these defensive adaptations, tortoises do not need to be able to move exceedingly quickly. Tortoises also have poor hearing, as good hearing is not a useful trait to the tortoise.

Most tortoises are herbivores, subsisting on flowers, leaves, fruit, grass, and weeds. Omnivorous species also eat insects and the remains of dead animals. Tortoises do not have teeth, and instead have a beak that they use to bite into leaves and vegetation.

Tortoises can vary greatly in size depending on species. The smallest tortoise, the speckled cape tortoise, measures 2.5-3.9 inches in length and 3.4-5.8 ounces in weight on average, and the largest tortoise, the giant tortoise, the Galapagos tortoise, may measure over 5 feet in length and up to 550 pounds in weight.

Females reproduce by laying multiple eggs at once into a shallow hole that they have dug. The eggs are incubated by the warmth of the sun or by a layer of rotting vegetation that the female may place over them.

Tortoises emerge fully formed and independent as they hatch from their shells. Young tortoises are solitary, fending for themselves and finding their own food. At this time, they are vulnerable to attack, and many do not survive their first few days. Tortoises that survive continue to be solitary in adult life.

Tortoises tend to have the longest lifespans of all animals, with some tortoises having lived for over 150 years. The oldest confirmed tortoise lived to be 176 years old, though some reports indicate that tortoises have lived even longer lives.