Hoplophobia is a political neologism coined by retired American military officer Jeff Cooper as a pejorative to describe an "irrational aversion to weapons." It is also used to describe the "fear of firearms" or the "fear of armed citizens." Hoplophobia is a political term and not a recognized medical phobia.

Phobias are a common form of anxiety disorders and distributions are heterogeneous by age and gender. An American study by the National Institute of Mental Health (NIMH) found that between 8.7 percent and 18.1 percent of Americans suffer from phobias, making it the most common mental illness among women in all age groups and the second most common illness among men older than 25. Between 4 percent and 10 percent of all children experience specific phobias during their lives, and social phobias occur in one percent to three percent of children and adolescents.

A Swedish study found that females have a higher incidence than males (26.5 percent for females and 12.4 percent for males). Among adults, 21.2 percent of women and 10.9 percent of men have a single specific phobia, while multiple phobias occur in 5.4 percent of females and 1.5 percent of males. Women are nearly four times as likely as men to have a fear of animals (12.1 percent in women and 3.3 percent in men) — a higher dimorphic than with all specific or generalized phobias or social phobias. Social phobias are more common in girls than in boys, while situational phobia occurs in 17.4 percent of women and 8.5 percent of men.

Rachman proposed three pathways to acquiring fear conditioning: classical conditioning, vicarious acquisition and informational/instructional acquisition.

Much of the progress in understanding the acquisition of fear responses in phobias can be attributed to classical conditioning (Pavlovian model). When an aversive stimulus and a neutral one are paired together, for instance when an electric shock is given in a specific room, the subject can start to fear not only the shock but the room as well. In behavioral terms, this is described as a conditioned stimulus (CS) "(the room)" that is paired with an aversive unconditioned stimulus (UCS) "(the shock)", which leads to a conditioned response (CR) "(fear for the room)" (CS+UCS=CR).

For instance, in case of the fear of heights (acrophobia), the CS is heights such as a balcony on the top floors of a high rise building. The UCS originates from an aversive or traumatizing event in the person's life, such as almost falling down from a great height. The original fear of almost falling down is associated with being on a high place, leading to a fear of heights. In other words, the CS "(heights)" associated with the aversive UCS "(almost falling down)" leads to the CR "(fear)".

This direct conditioning model, though very influential in the theory of fear acquisition, is not the only way to acquire a phobia.

Vicarious fear acquisition is learning to fear something, not by a subject's own experience of fear, but by watching others reacting fearfully (observational learning). For instance, when a child sees a parent reacting fearfully to an animal, the child can become afraid of the animal as well. Through observational learning, humans are able to learn to fear potentially dangerous objects; a reaction which also been observed in non-human primates. In a study focusing on non-human primates, results showed that the primates learned to fear snakes at a fast rate after observing parents’ fearful reactions. An increase of fearful behaviors was observed as the non-human primates continued to observe their parents’ fearful reaction. Even though observational learning has been proven to be effective in creating reactions of fear and phobias, it has also been shown that by physically experiencing an event, chances increase of fearful and phobic behaviors. In some cases, physically experiencing an event may increase the fear and phobia more so than observing a fearful reaction of another human or non-human primate.

Informational/instructional fear acquisition is learning to fear something by getting information. For instance, fearing electrical wire after having heard that touching it will result in an electric shock.

A conditioned fear response to an object or situation is not always a phobia. To meet the criteria for a phobia there must also be symptoms of impairment and avoidance. Impairment is defined as being unable to complete routine tasks whether occupational, academic or social. In acrophobia an impairment of occupation could result from not taking a job solely because of its location at the top floor of a building, or socially not participating in a social event at a theme park. The avoidance aspect is defined as behavior that results in the omission of an aversive event that would otherwise occur with the goal of the preventing anxiety.

American firearms expert and retired Marine colonel Jeff Cooper coined the word in 1962 to denigrate and anger proponents of gun control by implying that their thoughts were "aberrant" and unreasoning:

I coined the term "hoplophobia" in 1962 in response to a perceived need for a word to describe a mental aberration consisting of an unreasoning terror of gadgetry, specifically, weapons. The most common manifestation of hoplophobia is the idea that instruments possess a will of their own, apart from that of their user. This is not a reasoned position, but when you point this out to a hoplophobe he is not impressed because his is an unreasonable position. To convince a man that he is not making sense is not to change his viewpoint but rather to make an enemy. Thus hoplophobia is a useful word, but as with all words, it should be used correctly.

The term was constructed from the Greek ὅπλον – "hoplon", meaning, amongst other things, "arms," and φόβος – "phobos", meaning "fear." Cooper employed the term as just another alternative to other slang terms, stating: "We read of 'gun grabbers' and 'anti-gun nuts' but these slang terms do not [explain this behavior]." Cooper's conjecture was that "the most common manifestation of hoplophobia is the idea that instruments possess a will of their own, apart from that of their user." Writing in an opinion piece, "Pittsburgh Tribune-Review" columnist Dimitri Vassilaros said that the term was intended by Cooper as tongue-in-cheek to mock those who think guns have free will.