Pokemon is a series that focuses on the adventures of kids and teenagers as they attempt to capture Pocket Monsters - or Pokemon - and become masters at battling with them, forming a deep bond with the creatures which come in many species and elements. Most have the ultimate goal of fighting their way to the championship, but many are beseiged by the attempts of Team Rocket to conquer the planet and dominate the power of Pokemon.
However, this theme tosses off the shackles of the cutesy-wootsy canon of the series. Based loosely off the theme of Pokemon Champions MUSH, a loose-knit band of teenage trainers inspired by Professor Oak and with silent affiliation with the US military attempt to defeat the powerful gang, Team Rocket, headed by his old student, Giovanni. The Pokemon League, the regional and international power governing the use of Pokemon, has also moved to assist the trainers, providing them with needed supplies and personel where it can, deploring Team Rocket's theft and abuse of Pokemon and attempts at overrunning Kanto, the region the theme focuses on and jointly controlled by the US and the League. Key to the conflict is Ash - a trainer with great talents who unknowingly is the child of Giovanni and Delia, another one of Professor Oak's students - Gary, who is Professor Oak's grandson - and Richie, a genetic amalgamation made by Team Rocket to try to equal Ash and Gary's power.
Oak's group has stopped a number of attempts by Giovanni to dominate the world, first with Richie, and other times using the legendary Pokemon - rare Pokemon revered as almost godlike - against otherwise impossible odds. The trainers of this world, unlike their dimwitted anime counterparts, are helped by telepathic links with their Pokemon, allowing the trainer and Pokemon to be more deeply integrated and bonded more directly. This is bolstered by the fact that the trainers in the Kanto region seem to be able to utilize the power of the link, allowing them to unlock their hidden potential that would normally take many years of training to develop and grants them anime-like capabilities such as psionics, ki use and great martial arts skill. Numerous mysteries abound, as per the purpose of the legendaries, Team Rocket's true intentions, and just what Pokemon and humans are truly capable of.
Long story short, it's not a kid's show anymore.