Poké Balls

A Poké Ball is a type of item that is critical to a Trainer's quest, used for catching and storing Pokémon. In Pokémon Go, three varieties of Poké Balls exist:

Poké Balls are the most basic of them all and the ones with the lowest success rate in term of capture. These increase with the Great Ball and are their highest with Ultra Balls.

There are some references to the Master Ball in the game files, but there is no confirmation of it's existence in the game at this time.