Federal law requires that licensed firearm dealers run a background check on individuals seeking to purchase a gun. However, because the law does not extend to private sales, unlicensed dealers may sell individuals guns without running a background check, as often happens at gun shows, on the internet and between friends.
According to a study published in the journal Annals of Internal Medicine in 2017, nearly a quarter (22%) of American gun owners "obtained their most recent firearm within the previous two years without a background check."
Public opinion polls consistently find that more than 80% of Americans support expanded background checks for gun purchases. Twenty-one states and the District of Columbia have background-check or permit requirements that go beyond the federal rules.
A study published in the Journal of General Internal Medicine in 2019 found that "universal background checks were associated with an approximately 15% reduction in overall homicide rates."