A Pokédex (Japanese: ポケモン illustrated Pokémon encyclopedia) is an invaluable tool to a Trainer in the Pokémon world. It gives information about all Pokémon in the world that are contained in its database. In the games, it lists the number of Pokémon seen and caught. In the anime, simply pointing it at a target Pokémon will give someone the Pokédex entry for that Pokémon. In both the anime and Pokémon Special, the Pokédex also confers all the information shown by the interface in the games; that is, a Pokédex can display a Pokémon's stats, level, and moves. Another function of the Pokédex is that it is immune to most forms of outside interference from stimuli such as water, fire or electricity, as seen in The Misty Mermaid, in the Generation III games where the player can go under water, and in Pokémon, I Choose You!. Pokédexes in the games, anime, and manga are not given to all trainers, but given to trainers of exceptional potential and skill. Just the same, anime Pokédexes take the place of the trainer card in that they store the identification information of their owner. In the anime, Ash and Gary both received their Pokédexes from Prof. Oak, much like their game counterparts Red and Blue. Ash was notorious for using his Pokédex early in his journey in situations where he had no idea what was going on, and was just as notorious for always being behind Gary in Pokédex entries.
In the Pokémon continuity, the Pokédex was invented by Professor Oak. When a young "Sammy" Oak was accidentally warped to a future of his own time, Ash explains to him how the Pokédex works, unknowingly giving him an idea.
Pokédex entries are typically only two- or three-sentence bits of information about the Pokémon referred to. In some events it gives background information on the habitat or activities of this Pokémon in the wild; at other times it gives other bits of information on the Pokémon's history or anatomy. A typical entry would be one of Bulbasaur, which states:
"A strange seed was planted on its back at birth. The plant sprouts and grows with this Pokémon."
Though the technology behind the workings of a Poké Ball remains unknown, the basic mechanics are fairly simple to understand. In a battle, once the opposing wild Pokémon has been weakened, the Trainer will throw a Poké Ball at it. Assuming the Poké Ball hits it and is not dodged or hit back to the Trainer, the Poké Ball will open, convert the wild Pokémon to an energy form, pull the energy into its hollow center, and then close. The wild Pokémon will then be given the chance to struggle to try and escape the Poké Ball. If it escapes, in the anime, the Poké Ball flies back towards the Trainer, while in the games, the Poké Ball bursts open and cannot be reused. If it does not escape, the wild Pokémon will be caught.
As seen in anime episodes like Gulpin it Down! and Claydol Big and Tall, normal Poké Balls have difficulty catching extremely large and heavy Pokémon, to the point that the Pokémon will not even be taken entirely into the Poké Ball. The latter of these episodes shows how ancient civilizations overcame this issue: to catch and hold a very large Pokémon, they constructed a very large Poké Ball out of stone. However, giant stone Poké Balls are nearly impossible to use, so with the advancement of technology a better solution came in the form of Heavy Balls.
Besides catching new Pokémon, Poké Balls are also used to store caught Pokémon. A Trainer can have six Poké Balls with Pokémon in them at one time. When starting a battle, he or she can throw out one or more of these onto the battlefield, and they will open, releasing their Pokémon quickly. When a Trainer wants to recall their Pokémon, they simply hold up the Poké Ball and point it at their Pokémon, and a beam will come from the Poké Ball's button, converting the Pokémon into energy again and drawing it back in. If this beam hits a person for any reason, that person will be momentarily stunned. Also, some Pokémon know how to enter and leave their Poké Balls at will, several examples being Jessie's Seviper (only when Zangoose are involved), Jessie's Wobbuffet, May's Skitty, and more famously, Misty's Psyduck and Brock's Croagunk. Also, if a Pokémon is being sent out, but does not wish to exit its Poké Ball, when the flash of light emerges from the Poké Ball, it will make a u-turn back to the open ball, turn red, and re-enter the Poké Ball. This happened in Dig Those Diglett!, when Gary Oak attempted to send out several unnamed Pokémon to battle the wild Diglett. It also happened when Ash attempted to send out his Squirtle (though before he threw the ball, Pikachu yelled something to Squirtle), and when numerous Trainers attempted to send out their Pokémon. Poké Balls are not always at full size. Tapping the button on the front can convert it from full size, about the same size as a baseball, to a miniature size, about the same size as a ping-pong ball. This smaller size is more useful for storage, being small enough to carry in pockets or on belts.
Poké Balls presumably can communicate with a Trainer's Pokédex, since the system updates itself with new caught Pokémon information, and keeps track of how many full Poké Balls the Trainer has on-hand. If the Trainer catches a new Pokémon while their team of six is full, it will be transported to the Pokémon storage system they are using. They also have the ability to "mark" their catches - as shown in Two Degrees of Separation, when Dawn attempts to catch Ash's Pikachu - so that they cannot be caught by other Poké Balls once caught. This has shown some inconsistency in the series, particularly in older episodes such as in Bad to the Bone when Jessie throws a Poké Ball at Otoshi's Doduo which has to be reflected by Otoshi himself, like in the games.
When a Pokémon is released from its ball, it usually has a burst of light come out with it, which varies depending on the Ball the Pokémon is contained in (normally a white light in the anime). However, when a Ball Capsule and seals are used, visual effects will accompany the Pokémon's release. It has also been shown that if a Pokémon is sent out with a blue light, that Pokémon will be released and will be able to go back into the wild (in the anime, one can also break the Poké Ball, like in the cases of Brock and Jessie, while releasing Ninetales and Dustox, respectively.)