The United States (U.S.) is the most heavily armed society in the world, with about 90 guns for every 100 citizens. Although the U.S. is only about 4% of the world’s population, U.S. citizens possess about 31% of the world’s guns. Guns are easily purchased in the U.S. with little oversight or regulation. Indeed, you can make your own gun using a 3D printer.
The U.S. is unique among high-income countries with respect to the level of lethal violence, particularly gun violence. About 68% of murders in the U.S. are committed with guns (the next highest category is 13% with knives). Gun violence is a serious public health concern in the U.S. Each year there are about 30,000 gun-related deaths in the U.S. In fact, the number of gun-related deaths is projected to exceed the number of traffic-related deaths in the U.S. in 2015 The U.S. has the highest rate of gun fatalities among high-income countries—about 20 times the average for other high-income countries.
Although violent crime in the U.S. has been decreasing since the mid-1990s, school rampage shootings have increased. To protect children from school shooters, some companies have designed products such as bulletproof blankets, white boards, and backpacks. The Chief of the National Rifle Association (NRA) said, “The only thing that stops a bad guy with a gun is a good guy with a gun,” and that armed guards would make schools safer., However, the National Education Association has rejected the NRA’s claim and said that armed guards would make schools less safe rather than safer.
At least 19 states have introduced legislation to allow concealed weapons on college campuses, but a recent study found that 78% of college students oppose such legislation and 79% said they would feel less safe if faculty, students, and visitors carried concealed weapons on campus. Likewise 95% of college presidents oppose such legislation, and 91% cite accidental shootings of fellow students as the main reason why. Some campuses even have separate housing for college students with and without guns, such as the University of Colorado. Other states have passed laws that allow people to carry concealed weapons in public places. For example, in the state of Virginia you can carry guns inside banks, churches, restaurants, malls, schools, and other private businesses. However, visitors to the National Rifle Association (NRA) Headquarters building in Fairfax, Virginia are not allowed to bring guns inside (although visitors can shoot guns at the firing range in the basement of NRA Headquarters, which has a separate entrance). In the state of Iowa, even legally blind individuals can carry guns in public.
Why Do People Own Guns?
Most gun owners say they use the guns to protect themselves from criminals, for hunting, and for target practice. 
Males are about five times more likely than females to use guns for recreational purposes (e.g., target shooting, hunting). 
Some gun owners arm themselves because they don’t trust the government to protect them from outside sources, or because they are afraid the government will try to take their guns away. These individuals view the gun as an icon for democracy and personal empowerment. For example, some bumper stickers read: “"I'll give you my gun when you pry it from my cold, dead hands.”
The main reasons juvenile offenders give for carrying weapons is for self-protection. Some youth own guns to frighten others and gain respect, and these youth also have very high rates of antisocial behavior.  Especially in youth gangs, guns are used to project and protect a tough image.  Juvenile offenders aren’t the only ones who use guns to intimidate others. A U.S. survey found that guns in the home are more likely to be used by men to intimidate women than against strangers.
In the U.S., the Second Amendment allows people to legally possess guns. Some people believe that guns make people safer because they can protect themselves if attacked, whereas others believe that guns make people less safe. One recent study provided the first mathematical analysis of this tradeoff. The model compared two alternative scenarios on homicide rates: (1) a policy banning private possession of guns, and (2) a policy allowing the general population to carry guns. The results showed that a ban of private gun possession, or possibly a partial reduction in gun availability, might lower the rate of gun-related homicides.
Gun ownership is the strongest predictor of homicide in U.S. homes, even after controlling for other potential confounding factors (e.g., drug use, previous criminal record, history of violence).  Analysis of crime records found that people who had been shot with a gun were 4.5 times more likely than average to be carrying a gun themselves at the time.  Thus, guns did not protect those who possessed them from being shot. The increased availability of guns in a community is also related to the number of police officers killed by guns.  One additional problem with guns is that they can lead to rapid violent escalations.  Similar findings occur outside the home. For example, businesses that allow guns in the work place are about 5 times more likely to experience a homicide than businesses that do not.  For example, one Florida man was shot to death in a movie theater for texting on his phone during movie previews.
Research shows that background checks can reduce gun homicides. For example, one recent study found that gun-related homicides increased 25% after Missouri repealed its law requiring background checks, even after the researchers controlled for several other factors related to homicides (e.g., policing levels, incarceration rates, unemployment, poverty).
Although one can certainly kill people with other weapons (e.g., knives), one can kill more people much faster with guns than with other weapons. For example, the same day of the Newtown shooting a man stabbed 22 children in China, but none of them died. Guns also increase the physical and psychological distance between the killer and the victims, which makes killing much easier. When is the last time you heard of a drive-by stabbing?
Among people who successfully commit suicide, most used a gun, followed by ingested poisons, hangings, and inhaled poisons.  For example, one study found that 86% of suicides were committed with guns in homes with guns, whereas only 6% were committed with guns in homes without guns. People often use guns to commit suicide because they are faster, less painful, and more reliable than other means. (People seeking to survive an attempted suicide in order to get attention will typically avoid guns.) When gun control laws are passed, suicides due to guns decrease, with most studies showing no increase in suicide by other means. , These findings apply to countries other than the U.S.. For example, one study found that gun ownership was positively related to suicide rates in the U.S. and 20 other countries. Gun experts agree. A Harvard University survey found that 84% of firearms researchers either agree or strongly agree with the statement “In the United States, having a gun in the home increases the risk of suicide.”
One unintended cost of gun ownership is the increased risk of accidents, including fatal ones. Each year in the U.S. there are about 19,000 gun accidents, and about 600 of these are fatal. For example, at an Arizona shooting range called “Bullets and Burgers,” a 9-year-old girl accidentally shot and killed her shooting instructor when she lost control of the high-powered Uzi submachine gun she was firing.Accidents can even occur with BB guns and cap guns. Accidental gun deaths often occur in more rural areas among poorer families.  In U.S. homes that contain both children and firearms, 55% of the guns are loaded and unlocked. The American Academy of Pediatrics (AAP) recommends that gun owners unload and lock up guns to avoid accidents. To reduce the weapons effect, gun owners could not only follow AAP recommendations, but also keep guns out of sight of family members, rather than visibly displayed in glass cabinets or on shelves. 
The available evidence, though sparse, indicates that children who play with toy guns are more aggressive afterwards.  In one experiment,  for example, 4- to 5-year-old children were randomly assigned to play with toy guns or with toy airplanes. During a free play session, the children who played with guns were found to be more aggressive.
In summary, the main benefits of gun ownership are feeling safe, free, independent of the government, and powerful. However, the available data show that if you own a gun it is much more likely to be used to kill you (suicide) or someone you love (accident, homicide in a heated argument) than a stranger in self-defense. The costs of living in a society of gun owners also means a substantially higher rate of homicides, suicides, and accidents. To many social scientists, the costs of gun ownership far outweigh the benefits.
 MacInnis, L. (2007, August 28). U.S. most armed country with 90 guns per 100 people. Reuters News. Retrieved from http://www.reuters.com/article/2007/08/28/us-world-firearms-idUSL2834893820070828
 Schlessinger, R. (2013, December 31). The 2014 U.S. and world populations. U.S. News & World Report. Retrieved from http://www.usnews.com/opinion/blogs/robert-schlesinger/2013/12/31/us-pop...
 Memmott, M. (2013, May 6). Gun made with 3-d printer is successfully fired. NPR. Retrieved from http://www.npr.org/blogs/thetwo-way/2013/05/06/181612663/gun-made-with-3...
 Wellford, C. F., Pepper, J. V., & Petrie, C. V. (Eds.) (2013). Firearms and violence: A critical review. Washington, DC: The National Academies Press.
 FBI (2013) Uniform crime reports. Retrieved from http://www.fbi.gov/about-us/cjis/ucr/crime-in-the-u.s/2011/crime-in-the-...
 Kegler, S. R., & Mercy, J. A. (2013). Morbidity and mortality weekly report. Center for Disease Control and Prevention, 62(3), 597-602. Retrieved from http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6230a1.htm?s_cid=mm6230a1_w
 Christoff, C., & Kolet, I. (2012). American gun deaths to exceed traffic fatalities by 2015. Bloomberg. Retrieved fromhttp://www.bloomberg.com/news/2012-12-19/american-gun-deaths-to-exceed-traffic-fatalities-by-2015.html
 Fisher, M. (14 December 2012). Chart: The U.S. has far more gun-related killings than any other developed country. The Washington Post, Retrieved from http://www.washingtonpost.com/blogs/worldviews/wp/2012/12/14/chart-the-u-s-has-far-more-gun-related-killings-than-any-other-developed-country/
 Rocque, M. (2012). Exploring school rampage shootings: Research, theory, and policy. The Social Science Journal, 49(3), 304-313. DOI: 10.1016/j.soscij.2011.11.001
 Lichtblau, E., & Rich, M. (2013). N.R.A. envisions ‘a good guy with a gun’ in every school. New York Times. Retrieved from http://www.nytimes.com/2012/12/22/us/nra-calls-for-armed-guards-at-schoo...
 Thompson, A., Price, J. H., Dake, J. A., Teeple, K., Bassler, S., Khubchandani, J., Kerr, D., Fisher, J. B., Rickard, M., Oden, L., Aduroja, A., Lyde, A., Philips, K., Adeyanju, M., Eggleston, B., Ferng-Kuo, S.-K., Duquette, D., Bartholomew, K., & Stratton, C. (2013). Student perceptions and practices regarding carrying concealed handguns on university campuses. Journal Of American College Health, 61(5),243-253. DOI: 10.1080/07448481.2013.799478
 Price, J. H., Thompson, A., Khubchandani, J. Dake, J., Payton, E., & Teeple, K. (in press). University presidents’ perceptions and practice regarding the carrying of concealed handguns on college campuses. Journal Of American College Health DOI: 10.1080/07448481.2014.920336
 New York Times (2012, August 28). New man on campus, armed. Retrieved from http://www.nytimes.com/2012/08/29/opinion/new-man-on-campus-armed.html?_...
 Clayworth, J. (2013, September 8). Iowa grants gun permits to the blind. USA Today. Retrieved from http://www.usatoday.com/story/news/nation/2013/09/08/iowa-grants-gun-per...
 Carroll, J. (2005). Gun ownership and use in America. Gallup. Retrieved from http://www.gallup.com/poll/20098/gun-ownership-use-america.aspx
 Vittes, K. A., & Sorenson, S. B., (2005). Recreational gun use by California adolescents. Health Education & Behavior, 32(6), 751–766.
 Sheley, J. F., & Wright, J. D. (1993). Motivations for gun possession and carrying among serious juvenile offenders. Behavioral Sciences & the Law, 11(4), 375–388.
 Cunningham, P. B., Henggeler, S. W. Limber, S. P. Melton, G. B., & Nation, M. A. (2000). Pattern and correlates of gun ownership among nonmetropolitan and rural middle school students. Journal of Clinical Child Psychology, 29(3), 432–442.
 Azrael, D., & Hemenway, D. (2000). 'In the safety of your own home': Results from a national survey on gun use at home. Social Science & Medicine, 50(2), 285-291.
 Kellermann, A. L., Rivara, F. P., Rushforth, N. B., Banton, J. G., et al. (1993). Gun ownership as a risk factor for homicide in the home. The New England Journal of Medicine, 329(15), 1084–1091. But also see criticism by Kleck, G. (2001). Can owning a gun really triple the owner's chances of being murdered? The anatomy of an implausible causal mechanism. Homicide Studies, 5(1), 64-77. doi: 10.1177/1088767901005001005
 Branas, C. C., Richmond, T. S., Culhane, D. P., Ten Have, T. R., & Wiebe, D. J. (2009). Investigating the link between gun possession and gun assault. American Journal of Public Health, 99(11), 2034–2040.
 Lester, D. (1987). The police as victims: The role of guns in the murder of police. Psychological Reports, 60(2), 366.
 Phillips, S., & Maume, M. O. (2007). Have gun will shoot? Weapon instrumentality, intent, and the violent escalation of conflict. Homicide Studies: An Interdisciplinary & International Journal, 11(4), 272–294.
 Robles, F. (2014, January 13). Man Killed During Argument Over Texting at Movie Theater. New York Times. Retrieved from http://www.nytimes.com/2014/01/14/us/florida-man-is-shot-to-death-for-te...
 Webster, D., Kerccher Crifasi, C., & Vernick, J. S. (in press). Effects of Missouri’s repeal of its handgun purchaser licensing law on homicides. Journal of Urban Health.
 Kellermann, A. L., Rivara, F. P., Somes, G., Reay, D. T. et al. (1992). Suicide in the home in relation to gun ownership. The New England Journal of Medicine, 327(7), 467–472.
 Carrington, P. J., & Moyer, S. (1994). Gun control and suicide in Ontario. The American Journal of Psychiatry, 151(4), 606–608.
 Killias, M., Van Kesteren, J., & Rindlisbacher, M. (2001). Guns, violent crime, and suicide in 21 countries. Canadian Journal of Criminology, 43(4), 429–448.
 Harvard Injury Control Research Center (2014, May). Firearm researcher surveys. Retrieved from http://www.hsph.harvard.edu/hicrc/wp-content/uploads/sites/1264/2014/05/...
 Centers for Disease Control and Prevention (2010). Retrieved from http://www.cdc.gov/nchs/fastats/accidental-injury.htm
 Damore, D. T., Ramundo, M. L., Hanna, J. P., & Dayan, P. S. (2000). Parental attitudes toward BB and pellet guns. Clinical Pediatrics, 39(5), 281–284.
 Maze, D. A. E., & Holland, A. J. A. (2007). Cap gun burns in children. Journal of Paediatrics and Child Health, 43(7–8), 555–556.
 Ruddell, R., & Mays, G. L. (2004). Risky behavior, juveniles, guns, and unintentional firearms fatalities. Youth Violence and Juvenile Justice, 2(4), 342–358.
 Bushman, B. J. (2013). The weapons effect. JAMA Pediatrics, 167(12), 1094-1095. DOI:10.1001/jamapediatrics.2013.3824
 Watson, M. W., & Peng, Y. (1992). The relation between toy gun play and children’s aggressive behavior. Early Education and Development, 3(4), 370–389.
 Turner, C. W., & Goldsmith, D. (1976). Effects of toy guns and airplanes on children’s antisocial free play behavior. Journal of Experimental Child Psychology, 21(2), 303–315.