What is the IUCN system for determining threat status?

Question

Could somebody please outline for me what system IUCN uses to determine threat status of species' worldwide.

How do they label one animal as vulnerable and another as critically endangered?

What process do they go through to get to a conclusion of what status an animal (or plant) has?

Answer 1

HERE IS THE LINK

http://cms.iucn.org/about/work/programme...

Answer 2

This link might help:

http://www.mfe.govt.nz/publications/ser/...