Pokémon World

We can assume that the Pokemon anime, games and other stories take place on Earth, or some Earth-like world. Humans live on this planet alongside Pokemon as a human-animal relationship. Although it is unlikely, it may be that humans have inhabited anotehr planet somewhere else in the galaxy. Another suggestion put foward by fans it that the story may take place in a parralell Universe.

It is also assumed that it is set some time in the future, due to the fact that people use inhanced technology such as Pokeballs, teleportation (in the PC's) and robots (Team Rocket).

Animals have been mentioned many times such as when Ash caught his Caterpie, Misty mentioned that she hated bugs. She could be just referring to Bug-type Pokemon. But solid proof of common animals exsisting is the Pokedex entry for Gastly:

'''A being that exists as a thin gas. It can topple an Indian elephant by enveloping the prey in two seconds.'''

Surely, if there were no Earth animals on this planet then the Pokedex would surely refer to Indian Donphan perhpas instead of elephant.