While most American gun owner take their responsibilities seriously, the constant news reports about shootings demonstrate that dangerous people can access guns too easily. These dangerous people often obtain guns through a gap in our nation's gun laws -- the loophole for unlicensed sales -- which enables many gun sellers to avoid conducting background checks. This report describes how criminals and other dangerous people exploit this loophole in the federal law. They know that, in many states, they can attend a gun show or search online and easily find people willing to sell a gun without a background check. It doesn't have to be this way. Requiring a background check before the sale or transfer of a gun is a commonsense solution to this problem that respects the rights of law-abiding, responsible gun owners, and protects public safety. As of December 2014, the following 18 states have extended a background check requirement to at least some unlicensed gun sales. This product provides arguments in support of this proposal, along with the legal and factual background. It also provides a list of the features of a strong law on this topic. It is our hope that this report will provide a "toolkit" for legislators and advocates who want to move forward with closing the loopholes in the background check system in their states and communities.