Like in past Pokemon games, you are rewarded for completing your Pokedex by seeing or catching Pokemon. However, in Black 2 and White 2, you are rewarded with actual in-game items as opposed to the diploma of past games.

Award	How to unlock
License	See all Unova Pokedex
Round Charm	Catch all Unova Pokedex
Shining Charm	Catch all National Pokedex