Thirty-three states have “shall-issue” laws that require law enforcement authorities to issue permits to carry concealed weapons to any qualified applicant who requests one—that is, to adults with no documented record of significant criminality or mental illness. A spirited academic debate has emerged over whether these laws are helpful or harmful. While it is fairly easy to list the possible consequences of the passage of these laws, it has not been easy to come to agreement about which effects dominate in practice. Many scholars fear that these laws will stimulate more ownership and carrying of guns, leading to adverse effects such as an increase in spur-of-the-moment shootings in the wake of arguments or opportunistic criminal acts, increased carrying and quicker use of guns by criminals, more opportunities for theft of guns, thereby moving more legally owned guns into the hands of criminals, and more accidental killings and gun suicides. However, a path breaking article by John Lott and David Mustard in 1997 and a subsequent book by Lott have made the case that opportunistic crime should fall for everyone as criminals ponder whether they will be shot or otherwise thwarted by a potential victim or bystander carrying a concealed weapon.