There are actually several hundred species of geckos, and several are kept as pets.  The requirements and difficulty of care will vary with different species so it would be wise to know what you are getting and what will be needed to provide a good home for your gecko.  You should also consult multiple sources rather than relying on one source, as inconsistencies can sometimes be found between different sources.

Information is provided within these pages on the most popular kinds kept as pets: Leopard, African Fat-Tailed, Day, Madagascar Ground Geckos, and Tokay Geckos. 

Despite folklore to the contrary, a gecko's bite is not poisonous. Many species are arboreal, while others inhabit human dwellings. Most lack movable eyelids and have characteristic pads on the undersides of their feet that enable them to cling to smooth surfaces and to run upside down on ceilings. The pads contain microscopic backward-projecting hairs covered by tiny pads that may generate an adhesive force.

Geckos are animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Geckos come in a variety of beautiful patterns/colors depending on the species.  Most geckos are nocturnal (they are most active at night); they have large eyes and excellent vision.  They feed on small animals, chiefly insects. Nearly all lay eggs.

Geckos are unique among lizards in that they possess voices, and different species make characteristic sounds.  Some species of geckos make a squeaking or clicking noise that sounds like "gecko," hence their name.

The largest species is the 14-in. (35.5-cm) tokay, Gekko gecko, of SE Asia. The wall gecko, Tarentola mauritanica, of the Mediterranean region is commonly seen basking by day on walls and rocks; it hunts by night. There are two native species in the United States, the leaf-fingered gecko (Phyllodactylus tuberculatus) of extreme S California and Baja California, and the banded, or ground, gecko (Coleonyx variegatus) of the deserts of the SW United States and N Mexico. The latter is a ground-dwelling form and lacks foot pads. In Florida there are several introduced West Indian species as well as the widely distributed Turkish gecko, Hemidactylus turcicus, originally from Africa.

Never grab a gecko by the tail, for they will drop their tails (a natural defense against predators).
If this should happen, however, do not panic. It will grow back, although it may have a different shape and/or color. Geckos use the tail for fat storage, so the gecko should be well fed (and ideally separated from their cage mates) until the tail has regrown.