The Hunters Association

The Hunters Association is responsible for the testing and licensing of "Hunters," a person that has proven themselves through rigorous examination to be an elite member of humanity. With the passing of the examination, a Hunter is rewarded with a license to go almost anywhere in the world or do almost anything. Typically, Hunters devote themselves to tracking down priceless items, mystical places, and the unseen wonders of the world.

Hunter License
Hunter License is a type of card exclusively owned by Hunters after they passed the Hunter Examination. It proves the status of the owner and has multiple benefits.It also grants the ability to kill without facing any charges .

Becoming a Hunter
To become a Professional Hunter, two requirements have to be fulfilled: passing the Hunter Exam and learning how to use Nen.
more info please visit http://hunterxhunter.wikia.com/wiki/Hunters_Association
Note: the website is not mine