A paraphilia is intense and persistent sexual arousal or attraction to anything not sexual by nature. It has also been defined as a sexual interest in anything other than a legally consenting human partner. Paraphilias are contrasted with normophilic ("normal") sexual interests, although the definition of what makes a sexual interest normal or atypical remains controversial.

The exact number and taxonomy of paraphilia is under debate; Anil Aggrawal has listed as many as 549 types of paraphilias. Several sub-classifications of paraphilia have been proposed; some argue that a fully dimensional, spectrum, or complaint-oriented approach would better reflect the evident diversity of human sexuality. Although paraphilias were believed in the 20th century to be rare among the general population, subsequent research has indicated that some level of paraphilic interests are relatively common.

Coinage of the term paraphilia (paraphilie) has been credited to Friedrich Salomon Krauss in 1903, and it was used with some regularity by Wilhelm Stekel in the 1920s. The term comes from the Greek παρά (para), meaning 'other' or 'outside of', and φιλία (-philia), meaning 'loving'. The word was popularized by John Money in the 1980s as a non-pejorative designation for unusual sexual interests. It was first included in the DSM in its 1980 edition.

There is no broad scientific consensus for definitive boundaries between what are considered "unconventional sexual interests", kinks, fetishes, and paraphilias. As such, these terms are often used loosely and interchangeably, especially in common parlance.

Many terms have been used to describe atypical sexual interests, and there remains debate regarding technical accuracy and perceptions of stigma. John Money described paraphilia as "a sexuoerotic embellishment of, or alternative to the official, ideological norm". Psychiatrist Glen Gabbard writes that despite efforts by Wilhelm Stekel and John Money, "the term paraphilia remains pejorative in most circumstances."

In the late 19th century, psychologists and psychiatrists began to categorize various paraphilias so as to have a more descriptive system than the legal and religious constructs of sodomy, as well as perversion. In 1914, Albert Eulenburg observed a commonality across paraphilias, using the terminology of his time writing, "All the forms of sexual perversion ... have one thing in common: their roots reach down into the matrix of natural and normal sex life; there they are somehow closely connected with the feelings and expressions of our physiological erotism. They are ... hyperbolic intensifications, distortions, monstrous fruits of certain partial and secondary expressions of this erotism which is considered 'normal' or at least within the limits of healthy sex feeling."

Before the introduction of the term paraphilia in the DSM-III (1980), the term sexual deviation was used to refer to paraphilias in the first two editions of the manual. In 1981, an article published in American Journal of Psychiatry described paraphilia as "recurrent, intense sexually arousing fantasies, sexual urges, or behaviors generally involving":

Clinical literature contains reports of many paraphilias, only some of which receive separate entries in the diagnostic taxonomies of the American Psychiatric Association or the World Health Organization. There is disagreement regarding which sexual interests should be deemed paraphilic disorders versus normal variants of sexual interest. The DSM-IV-TR also acknowledges that the diagnosis and classification of paraphilias across cultures or religions "is complicated by the fact that what is considered deviant in one cultural setting may be more acceptable in another setting". Some argue that cultural relativism is important to consider when discussing paraphilias because there is wide variance concerning what is sexually acceptable across cultures. Consensual adult activities and adult entertainment involving sexual roleplay; novel, superficial, or trivial aspects of sexual fetishism; or incorporating the use of sex toys are not necessarily paraphilic.