Created in 2008, the index assesses the legality of purchase and possession of pistols, rifles, shotguns, fully automatic weapons, and suppressors, the legality of accessible home storage of at least one firearm for self-defense, and the legality of open and concealed carry of firearms of 235 nations and semi-autonomous regions. As it is the first attempt to quantify worldwide gun laws of its kind, there is some reliance on anecdotal evidence and news reports in lieu of direct legal analysis due to lack of access to primary sources (i.e., the actual written laws of some nations).
In 2009, Montana was tied with Yemen as the most permissive with regard to purchase, possession, and open carry of firearms, both scoring 9.0 out of 10 possible points.
As of the 2011 index, Arizona had risen to the top of the index with 9.3 out of 10 possible points as a result of the Arizona Firearm Freedoms Act being signed into law. However, the authors of the index caution that Arizona's law is in conflict with federal law pending the outcome of the Montana Shooting Sports Association v. Holder case. See: Montana Firearms Freedom Act.
On the national level, Yemen (which again in 2011 scored 9.0) had the most liberal firearm laws, with the United States and East Timor tied for second place with scores of 8.0. In contrast, the most restrictive gun laws could be found in Libya, Palau, the Solomon Islands, and Uganda, all of which scored 0.0 out of 10 in the index due to their outright bans on private firearm ownership.