Two things that reptiles and amphibians have in common is that they both have a backbone and they both are primarily cold-blooded animals. The leatherback sea turtle, which is a reptile, is an exception to the cold-blooded characteristic.
An animal that is cold-blooded changes its temperature with its surroundings. It does not continually maintain the same body temperature. A warm-blooded animal tries to maintain the same temperature at all times, regardless of its climate's temperature. Reptiles and amphibians have a lower body temperature when the temperature is low; this drop in body temperature causes reptiles and amphibians to be less active in cold weather. The leatherback sea turtle maintains its body temperature to a certain degree, but not to the extent that traditional warm-blooded animals can.
If an animal has a backbone, it is known as a vertebrate. An animal without a backbone is classified as an invertebrate. Amphibians and reptiles are both classified as vertebrates.
The defining characteristics of amphibians is that they spend their lives on water and land, have permeable skin and have gills for part of their life. Many amphibians undergo a process known as metamorphosis.
Two unique characteristics of a reptile is that it is covered with scales and breathes through its lungs. This is different than an amphibian that uses its skin to exchange gases and molecules. Most reptiles lay eggs when reproducing.