The IIHS, a private organization, gets a lot of notoriety because it issues the Top Safety Pick award each year within its class. This is determined by a total of five different crash tests. As a vehicle goes through these, it receives the rating of Poor, Marginal, Acceptable, or Good.
The NHTSA, which is an organization of the federal government, uses star ratings when it conducts a total of three different crash tests. Each vehicle is tested for frontal impact, side-impact, as well as a rollover. This allows you to see how safe a vehicle is in the event of getting into any kind of accident.