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:

Normal Poké Balls are the most common and have the lowest success rate in term of capture. The rate increases with the Great Ball, and above.

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