It is not uncommon in the toy industry for a new product to unexpectedly take the world by storm -- in fact, it can happen once or twice each year. Cabbage Patch Kids, Beanie Babies, Tickle Me Elmo -- these are all examples of toys that had an initial demand that totally overwhelmed the supply. Tamagotchis, the "virtual" creatures released by Bandai in Japan in 1996, and the United States in 1997, are another example of such an overnight sensation.

Compact, colorful, collectable, portable, and inexpensive, the first Tamagotchis were, as their story went, chicken-like "cyber pets" from the planet Tamagotchi. They had crash-landed on Earth, and each lived on a small LCD screen inside an egg-shaped plastic key chain case. These pets hatched on-screen, and needed their owner's care and attention to live and grow.

Tamagotchis are supposed to behave like real creatures, so they get hungry, dirty and bored, and need their owners to feed, clean, play with, and, in some instances, discipline them. As a Tamagotchi gets older, it morphs into other characters, depending on how well its owner is taking care of it. At the end of its short life (the record life span of a Tamagotchi is only 26 days), the creature either "returns to its home planet," according to Bandai, or dies, which is many people's interpretation of the final image of an angel that announces the Tamagotchi has gone. Once a Tamagotchi has moved on to a better place, a new one can be hatched at the touch of a button.

To make them as realistic as possible, Tamagotchis come with a built-in clock that must be set when they are "born," and their behavior changes depending on what time of day it is. For example, Tamagotchis are much more active during the day, preferring to sleep at night. Of course, the earliest virtual pets had little regard for their owners' schedules, and would beep for attention at any time of the day or night. Some versions now come with a "pause" feature that lets them be turned off temporarily while their owners sleep or go to school or work.

Nothing profitable ever goes un-duplicated in the toy industry, and it wasn't long before virtual pet "clones" crowded the shelves at toy stores. Many of these had the same attributes as the original Tamagotchis: They featured a creature that was born, lived and died (or left for someplace else), and needed to be cared for by its owner. Hidden characters and special features were also something common to many virtual pets, and were another Tamagotchi first.

With all this competition, the virtual pet industry saw an explosion of products, and innovations followed fast and furious. For example, the initial variety of virtual pets was limited to birds, cats, dogs, babies, and dinosaurs, and the toys themselves were aimed at a young, female audience. Now there are virtual pet versions of monsters, people, angels, insects, aliens and more, aimed at boys and girls alike. There are virtual versions of characters from the "Star Wars" movies, "101 Dalmatians," "Rugrats," "Babe," "The Little Mermaid," "Sabrina: The Teenage Witch," and the Loony Tunes cartoons. There are virtual pets that can be linked together, either for combat or to meet, fall in love, mate, and reproduce. Some virtual pets know when their case is being shaken, and some have touch-sensitive screens. There are even some virtual pets that recognize voice commands, and some that can respond in kind.

At the rate that new virtual pets are hitting the market, and with the loyalty and repeat business these digital marvels inspire, there is no sign of the market slowing down any time soon. With the wide variety of digital pets to chose from, it is safe to say there is one out there for almost everyone.