Concealed Carry Permit Laws by State Source: "Concealed Carry Permit Information by State," usacarry.com, (accessed Sep. 9, 2015)
Carrying a concealed handgun in public has been permitted in all 50 states since 2013, when Illinois became the last state to enact concealed carry legislation. Some states require gun owners to obtain permits while others have "unrestricted carry" and do not require permits. 
Proponents of concealed carry say that criminals are less likely to attack someone they believe to be armed. They cite the 2nd Amendment's "right of the people to keep and bear arms," and argue that most adults who legally carry a concealed gun are law-abiding and do not misuse their firearms.
Opponents of concealed carry argue that increased gun ownership leads to more gun crime and unintended gun injuries. They contend that concealed handguns increase the chances of arguments becoming lethal, and that society would be safer with fewer guns on the street, not more.
Categories of Permits
State regulations on concealed carry fall into four categories. The first is "no-issue," which does not allow citizens to carry a concealed handgun. The second category is "may-issue," which grants concealed carry permits at the discretion of local authorities. The third category is "shall-issue," which requires police to issue concealed carry permits as long as the applicant meets certain minimum requirements such as a minimum age, no prior felony conviction, and no recent commitments to a mental institution. The fourth category is "unrestricted carry," where no permit is required to carry a concealed handgun. 
In 1813 Kentucky and Louisiana passed the first laws prohibiting the concealed carrying of deadly weapons.  By 1850 most Southern states had prohibited concealed carry in an attempt to reduce high murder rates.  In the 1880s, non-Southern states began restricting the concealed carry of weapons.  After WWI, the focus of gun control efforts switched from the state to the federal level. Congress imposed an excise tax on weapons in 1919 and prohibited the shipping of handguns through the US postal system in 1927. In 1934 the federal government began regulating possession of weapons with the National Firearms Act.  "May-issue" laws were dominant in the post-World War II period.
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Gun owners rally at the Illinois State Capitol in support of proposed legislation to allow concealed carry. Source: Seth Perlman, "The Debate Over Gun Rights," www.csmonitor.com Mar. 11, 2009
In 1989 the National Rifle Association (NRA) launched a nationwide campaign to increase the number of states with "shall-issue" laws. At the time nine states had such laws, including Vermont (1903), New Hampshire (1923), Washington (1961), Connecticut (1969), Indiana (1980), Maine (1985), North Dakota (1985), South Dakota (1986), and Florida (1987). 
Intensive lobbying of state legislators by the NRA increased the number of shall-issue states from nine in 1987 to 30 by the year 2000.  Four of these "shall-issue" states (Alaska, Arkansas, Arizona, and Wyoming) are considered "constitutional carry," states where they allow for concealed carry without a permit as long as the person is legally able to own a firearm.  Those "constitutional carry" states can issue permits for non-residents and for residents traveling out of state.  Vermont, also considered a "shall-issue" state, does not issue permits at all. Its laws are sometimes referenced as "Vermont carry."  Eight states (CA, CT, DE, HI, MD, MA, NJ, NY) have "may-issue" laws which give law enforcement discretion in issuing permits (as of Mar. 14, 2014). 
Impact of "Shall-Issue" Laws on Crime
In 1998 John Lott, PhD, published More Guns, Less Crime which concluded that the "shall-issue" laws correlated with a decrease in violent crime. Lott argued that if states that did not permit concealed handguns in 1992 had permitted them in 1977, 1,570 murders, 4,177 rapes, 60,000 aggravated assaults, and 12,000 robberies would have been prevented between 1977 and 1992. 
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Sign posted on a Hermann, MO, courthouse forbidding the carrying of concealed guns. Source: "A Sign Of No Concealed Guns Allowed," www.worldofstock.com (accessed Mar. 29, 2010)
Following the release of Lott's book, researchers began issuing studies both supporting and criticizing Lott's results. An Oct. 2001 peer-reviewed study found that concealed carry had a deterrent effect on crime in some states and contributed to increases in crime in other states.  In Apr. 2003, Ian Ayres, PhD, and John Donohue, PhD, wrote in a peer-reviewed study published in the Stanford Law Review that "small increases in crime associated with the adoption of shall-issue laws."  However, Carlisle Moody, PhD, and Thomas Marvell, PhD, concluded in a Feb. 2008 study that a "shall-issue law is generally beneficial with respect to its overall long run effect on crime."  The National Research Council, the working arm of the National Academy of Sciences, concluded in 2004 that "it is impossible to draw strong conclusions from the existing literature on the causal impact of these laws." 
Concealed Handguns and the Second Amendment
The Second Amendment features prominently in the concealed handgun debate. The Second Amendment states (in its entirety), "A well regulated Militia being necessary to the security of a free State, the right of the people to keep and bear Arms shall not be infringed." In 1897, the US Supreme Court ruled in Robertson v. Baldwin that "the right of the people to keep and bear arms is not infringed by laws prohibiting the carrying of concealed weapons."  On June 26, 2008, the US Supreme Court ruled 5 to 4 in District of Columbia v. Heller that the Second Amendment guarantees "the individual right to possess and carry weapons in case of confrontation.This meaning is strongly confirmed by the historical background of the Second Amendment."  The US Supreme Court ruled 5 to 4 in McDonald v. Chicago on June 28, 2010 that the findings in District of Columbia v. Heller apply to the state and local governments in addition to federal jurisdictions like DC. 
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Political cartoon illustrating a pro-concealed carry argument. Source: Scott Bieser, "Gun Free Zone," www.nationalgunrights.org, 2007
President Obama and Guns
Following the election of President Barack Obama in Nov. 2008, Ohio issued 56,691 new concealed weapon permits in 2009, a 67% increase from the 33,864 licenses issued in 2008.  According to Jim Irvine, chairman of the Buckeye Firearms Association, this increase in concealed weapon permits is a result of "President Obama being anti-gun and the fear that he was going to do something to affect gun ownership." The Brady Campaign to Prevent Gun Violence gave President Obama an "F” rating for his first year in office for his efforts on gun control, in part because Obama signed the Credit Card Accountability Responsibility and Disclosure Act of 2009 on May 22, 2009 which included an amendment to allow the carrying of firearms in national parks.  The National Rifle Association also gave presidential candidate Barack Obama an "F" rating on gun rights.  Obama was quoted in an Apr. 2, 2008 article saying, "I am not in favor of concealed weapons. I think that creates a potential atmosphere where more innocent people could (get shot during) altercations." 
States and counties frequently restrict where concealed weapons can be carried to exclude schools, government buildings, and establishments where alcohol is served. Some states allow businesses to post signs prohibiting the carrying of concealed firearms within the establishment.
On July, 22, 2009, the US Senate rejected a bill in a 58 to 39 vote (60 votes were needed) by Sen. John Thune (R-SD) that would allow an individual who holds a concealed weapons permit in one state to travel with a loaded concealed weapon to any of the other 47 states that also issued permits at the time. 
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Children protest at Seattle's Pike Place Market over Starbucks' policy of allowing the open carrying of guns in stores. Source: Joshua Trujillo, "Starbucks Sticks to its Guns," www.seattlepi.com, Mar. 3, 2010
On July 8, 2011, Wisconsin became the 49th state to allow concealed carry.  Wisconsin citizens who go through training and obtain a permit are able to carry a concealed handgun in most public buildings and private businesses (including bars and churches) unless establishments post a sign forbidding it. On Dec. 11, 2012, the 7th Circuit Court of Appeals in Moore v. Madigan struck down an Illinois state law passed in 1962 that prohibited carrying a gun in public. On July 9, 2013, Illinois legislators overrode the governor's veto and passed a bill allowing concealed handguns. The law permits residents to purchase a concealed-carry license for $150 ($300 for non-residents) if they are 21 or older, pass a background check, complete 16 hours of gun safety training, and are not addicted to narcotics. 
Seven states allow carrying a concealed weapon on public college or university campuses, 21 states ban concealed weapons on campus, and 22 leave the decision up to the individual college or university.  In 2013, 19 states introduced legislation to allow carrying concealed weapons on campus. Two bills passed, one in Kansas that allows concealed carry for everyone and one in Arkansas that allows university faculty only to carry handguns.  Five states introduced legislation in 2013 to prohibit carrying concealed weapons on campus, but none of the bills passed. 
On July 26, 2014, Senior US District Court Judge Frederick J. Scullin Jr. overturned Washington, DC's complete ban on carrying handguns outside the home for self-defense. On Oct. 23, 2014 the District of Columbia began accepting concealed carry permit applications,   and is now officially a "may issue" area for concealed handgun permits.