Paraphilia (previously known as sexual perversion and sexual deviation) is the experience of intense sexual arousal to atypical objects, situations, fantasies, behaviors, or individuals. Such attraction may be labeled sexual fetishism. No consensus has been found for any precise border between unusual sexual interests and paraphilic ones. There is debate over which, if any, of the paraphilias should be listed in diagnostic manuals, such as the "Diagnostic and Statistical Manual of Mental Disorders" (DSM) or the International Classification of Diseases (ICD).

The number and taxonomy of paraphilia is under debate; one source lists as many as 549 types of paraphilia. The DSM-5 has specific listings for eight paraphilic disorders. Several sub-classifications of the paraphilias have been proposed, and some argue that a fully dimensional, spectrum or complaint-oriented approach would better reflect the evidence.

Voyeurism is the sexual interest in or practice of spying on people engaged in intimate behaviors, such as undressing, sexual activity, or other actions usually considered to be of a private nature.

The term comes from the French "voir" which means "to see". A male voyeur is commonly labeled as "Peeping Tom" or a "Jags", a term which originates from the Lady Godiva legend. However, that term is usually applied to a male who observes somebody secretly and, generally, not in a public place.

In the DSM-5 all paraphilia disorders can be diagnosed by two main criteria that are referred to criteria A and criteria B respectively. The A and B criteria include a duration in which the behavior must be present for (typically 6 months) and specific details of actions or thoughts that are correlated specifically with the respective disorder being diagnosed.

The DSM-5 adds a distinction between "paraphilias" and "paraphilic disorders", stating that paraphilias do not require or justify psychiatric treatment in themselves, and defining "paraphilic disorder" as "a paraphilia that is currently causing distress or impairment to the individual or a paraphilia whose satisfaction has entailed personal harm, or risk of harm, to others".

The DSM-5 Paraphilias Subworkgroup reached a "consensus that paraphilias are not "ipso facto" psychiatric disorders", and proposed "that the DSM-V make a distinction between "paraphilias" and paraphilic "disorders". [...] One would "ascertain" a paraphilia (according to the nature of the urges, fantasies, or behaviors) but "diagnose" a paraphilic disorder (on the basis of distress and impairment). In this conception, having a paraphilia would be a necessary but not a sufficient condition for having a paraphilic disorder." The 'Rationale' page of any paraphilia in the electronic DSM-5 draft continues: "This approach leaves intact the distinction between normative and non-normative sexual behavior, which could be important to researchers, but without automatically labeling non-normative sexual behavior as psychopathological. It also eliminates certain logical absurdities in the DSM-IV-TR. In that version, for example, a man cannot be classified as a transvestite—however much he cross-dresses and however sexually exciting that is to him—unless he is unhappy about this activity or impaired by it. This change in viewpoint would be reflected in the diagnostic criteria sets by the addition of the word "Disorder" to all the paraphilias. Thus, Sexual Sadism would become Sexual Sadism Disorder; Sexual Masochism would become Sexual Masochism Disorder, and so on."

Bioethics professor Alice Dreger interpreted these changes as "a subtle way of saying sexual kinks are basically okay – so okay, the sub-work group doesn’t actually bother to define paraphilia. But a paraphilic disorder is defined: that’s when an atypical sexual interest causes distress or impairment to the individual or harm to others." Interviewed by Dreger, Ray Blanchard, the Chair of the Paraphilias Sub-Work Group, explained: "We tried to go as far as we could in depathologizing mild and harmless paraphilias, while recognizing that severe paraphilias that distress or impair people or cause them to do harm to others are validly regarded as disorders."

Charles Allen Moser pointed out that this change is not really substantive as DSM-IV already acknowledged a difference between paraphilias and non-pathological but unusual sexual interests, a distinction that is virtually identical to what is being proposed for DSM-5, and it is a distinction that, in practice, has often been ignored. Linguist Andrew Clinton Hinderliter argued that "Including some sexual interests—but not others—in the DSM creates a fundamental asymmetry and communicates a negative value judgment against the sexual interests included," and leaves the paraphilias in a situation similar to ego-dystonic homosexuality, which was removed from the DSM because it was realized not to be a mental disorder.

The DSM-5 acknowledges that many dozens of paraphilias exist, but only has specific listings for eight that are forensically important and relatively common. These are voyeuristic disorder, exhibitionistic disorder, frotteuristic disorder, sexual masochism disorder, sexual sadism disorder, pedophilic disorder, fetishistic disorder, and transvestic disorder. Other paraphilias can be diagnosed under the Other Specified Paraphilic Disorder or Unspecified Paraphilic Disorder listings, if accompanied by distress or impairment.

Psychosexual disorder is a term which may simply refer to a sexual problem that is psychological, rather than physiological in origin. "Psychosexual disorder" was a term used in . The term of psychosexual disorder (Turkish: "Psikoseksüel bozukluk") used by the TAF for homosexuality as a reason to ban the LGBT people from military service.

Courtship disorder is a theoretical construct in sexology in which a certain set of paraphilias are seen as specific instances of anomalous courtship instincts in men. The specific paraphilias are biastophilia (paraphilic rape), exhibitionism, frotteurism, telephone scatologia, and voyeurism. According to the "courtship disorder hypothesis", there is a species-typical courtship process in human males consisting of four phases, and anomalies in different phases result in one of these paraphilic sexual interests. That is, instead of being independent paraphilias, this theory sees these sexual interests as individual symptoms of a single underlying disorder.

Underwear fetishism is a sexual fetishism relating to undergarments, and refers to preoccupation with the sexual excitement of certain types of underwear, including panties, stockings, pantyhose, bras, or other items. Some people experience sexual excitement from wearing, while others get their excitement when observing or handling the underwear worn by another, or watching somebody putting underwear on/taking it off. Some may steal used underwear to get satisfaction. Not only does this include physical contact with the garment(s), or their wearers, but also includes arousal by printed or electronic image with depictions of underwear.

Underwear fetishism is not considered as paraphilia unless it causes distress or serious problems for the person or those associated with them.

The American Psychiatric Association has classified certain voyeuristic fantasies, urges and behavior patterns as a paraphilia in the "Diagnostic and Statistical Manual" (DSM-IV) if the person has acted on these urges, or the sexual urges or fantasies cause marked distress or interpersonal difficulty. It is described as a disorder of sexual preference in the ICD-10. The DSM-IV defines voyeurism as the act of looking at "unsuspecting individuals, usually strangers, who are naked, in the process of disrobing, or engaging in sexual activity". The diagnosis would not be given to people who experience typical sexual arousal simply by seeing nudity or sexual activity. In order to be diagnosed with voyeuristic disorder the symptoms must persist for over six months and the person in question must be over the age of 18.

Candaulism is a sexual practice or fantasy in which a man exposes his female partner, or images of her, to other people for their voyeuristic pleasure.

The term may also be applied to the practice of undressing or otherwise exposing a female partner to others, or urging or forcing her to engage in sexual relations with a third person, such as during a swinging activity. Similarly, the term may also be applied to the posting of personal images of a female partner on the internet or urging or forcing her to wear clothing which reveals her physical attractiveness to others, such as by wearing very brief clothing, such as a microskirt, tight-fitting or see-through clothing or a low-cut top.

Downblouse is a form of sexual fetishism or voyeurism involving watching a person's breasts while looking down their dress. It may take the form of making unauthorized photographs down the top of a person's dress, blouse or other garment, capturing an image of their breasts or cleavage.

The practice is regarded as a form of sexual fetishism or voyeurism and is similar in nature to upskirting. With the advent of digital photography and camera phones, covert photography of cleavage became popular with some websites becoming dedicated to such photographs. A number of American and Australian states and Germany have specific statutes that prohibit such photography.

The ethical and legal issues relating to downblouse photography are also that of upskirt photography. The practice is regarded as an invasion of privacy of the person observed or photographed in this manner, as harassment and as an attack on their dignity.

Attraction to disability or devotism is a sexualised interest in the appearance, sensation and experience of disability. It may extend from normal human sexuality into a type of sexual fetishism. Sexologically, the pathological end of the attraction tends to be classified as a paraphilia. (Note, however, that the very concept "paraphilia" continues to elude satisfactory definition and remains a subject of ongoing debate in both professional and lay communities) Other researchers have approached it as a form of identity disorder. The most common interests are towards amputations, prosthesis, and crutches.

Until the 1990s, it tended to be described mostly as acrotomophilia, at the expense of other disabilities, or of the wish by some to pretend or acquire disability. Bruno (1997) systematised the attraction as factitious disability disorder. A decade on, others argue that erotic target location error is at play, classifying the attraction as an identity disorder. In the standard psychiatric reference "Diagnostic and Statistical Manual of Mental Disorders", text revision (DSM-IV-tr), the fetish falls under the general category of "Sexual and Gender Identity Disorders" and the more specific category of paraphilia, or sexual fetishes; this classification is preserved in DSM-5.

According to the "courtship disorder hypothesis", there is a species-typical courtship process in humans consisting of four phases. These phases are: "(1) looking for and appraising potential sexual partners; (2) pretactile interaction with those partners, such as by smiling at and talking to them; (3) tactile interaction with them, such as by embracing or petting; (4) and then sexual intercourse."

The associations between these phases and these paraphilias were first outlined by Kurt Freund, the originator of the theory: A disturbance of the search phase of courtship manifests as voyeurism, a disturbance of the pretactile interaction phase manifests as exhibitionism or telephone scatologia, a disturbance of the tactile interaction phase manifests as toucheurism or frotteurism, and the absence of the courtship behavior phases manifests as paraphilic rape (i.e., biastophilia). According to Freund, these paraphilias "can be conceptualized as a preference for a pattern of behavior or erotic fantasy in which one of these four phases of sexual interaction is intensified and distorted to such an extent that it appears to be a caricature of the normal, while the remaining phases are either omitted entirely or are retained only in a vestigial way."

Freund noted that "troilism" (a paraphilia for observing one’s sexual/romantic partner sexually interacting with a third party, usually unbeknownst to the third party) might also be a courtship disorder, troilism being a variant of voyeurism.

Appropriate behaviors depend on the social and cultural context, including time and place. Some behaviors that are unacceptable under most circumstances, such as public nudity or sexual contact between dancers, may be accepted or even encouraged during celebrations like Carnival or Mardi Gras. Where such cultural festivals alter normative courtship behaviors, the signs of courtship disorder may be masked or altered.

To determine relative prevalences of different fetishes, Italian researchers obtained an international sample of 5,000 individuals from 381 fetish-themed discussion groups. The relative prevalences were estimated based on (a) the number of groups devoted to a particular fetish, (b) the number of individuals participating in the groups and (c) the number of messages exchanged. Within the sample population (a population of adults online involved in sexual discussion), 12 percent indicated a fetish related to an "object associated with the body + external event" . This includes, but is not limited to, objects such as underwear, socks, shoes, etc. (see Table 1 in the .pdf of the first article cited).

Isidor Sadger hypothesized that the candaulist completely identifies with his partner's body, and deep in his mind is showing himself. Candaulism is also associated with voyeurism and exhibitionism. An alternative definition proposes it as a practice involving one person observing, often from concealment, two others having sexual relations.

Individuals with scopophobia generally exhibit symptoms in social situations when attention is brought upon them like public speaking. Several other triggers exist to cause social anxiety. Some examples include: Being introduced to new people, being teased and/or criticized, embarrassing easily, and even answering a cell phone call in public.

Often scopophobia will result in symptoms common with other anxiety disorders. The symptoms of scopophobia include an irrational feelings of panic, feelings of terror, feelings of dread, rapid heartbeat, shortness of breath, nausea, dry mouth, trembling, anxiety and avoidance. Other symptoms related to scopophobia may be hyperventilation, muscle tension, dizziness, uncontrollable shaking or trembling, excessive eye watering and redness of the eyes.

Building on Freud's concept of the eye as an erogenous zone, psychoanalysts have linked scopophobia to a (repressed) fear of looking, as well as to an inhibition of exhibitionism. Freud also referred to scopophobia as a "dread of the evil eye" and "the function of observing and criticizing the self" during his research into the "eye" and "transformed I's."

In some explanations, the equation of being looked at with a feeling of being criticized or despised reveals shame as a motivating force behind scopophobia. In the self-consciousness of adolescence, with its increasing awareness of the Other as constitutive of the looking glass self, shame may exacerbate feelings of erythrophobia and scopophobia.