Heterosexuality is a sexual orientation characterized by romantic love or sexual desire exclusively for members of the opposite sex or gender, contrasted with homosexuality and distinguished from bisexuality and asexuality.
In addition to referring to a sexual orientation, the term heterosexuality or heterosexual may also refer to sexual behavior or sexual activities between people of the opposite gender, regardless of sexual orientation.
Some people identify themselves as heterosexual even though they may engage in sexual activity with both men and women (whether occasionally or regularly).
Heterosexualism is sometimes used as a synonym for heterosexuality (that is, a sexual orientation or behavior). However, heterosexualism (not heterosexuality) is also used in a different sense, to refer to heterosexism (the idea that heterosexuality is superior or normal).
Hetero- comes from the Greek word heteros, meaning "different" (for other uses, see heterozygote, heterogeneous), and the Latin for sex (that is, physical sexual differentiation). The term "heterosexual" was coined shortly after and opposite to the word "homosexual" by Karl Maria Kertbeny in the 1860s.  "Heterosexual" was first listed in Merriam-Websters's New International Dictionary as a medical term for "morbid sexual passion for one of the opposite sex", but in 1934 in their Second Edition Unabridged it is a "manifestation of sexual passion for one of the opposite sex; normal sexuality". (Katz, 1995)
The history of heterosexuality is part of the history of sexuality.
Psychological factors relating to sexuality
Main article: Causes of sexual orientation
A broad array of opinion holds that much human behavior ultimately is explainable in terms of natural selection. From this point of view, the reason why humanity as a whole exhibits a strong statistical tendency towards heterosexuality is that heterosexual intercourse has the potential for producing offspring and homosexual intercourse does not.
In traditional societies individuals are often under heavy social pressure to marry and have children, irrespective of their sexual orientation. On the other hand many homosexuals wish for children, and some have found a way to procreate in spite of their sexual preference, generally through artificial or natural insemitation.
Not all people who are attracted or have sexual relationships with members of the opposite sex identify themselves as heterosexual: people who do not identify primarily as heterosexual may sometimes engage in heterosexual behaviour. Similarly, some people frequently have sex with members of the same sex yet still see themselves as heterosexual.
According to American Psychiatric Association (APA), there are numerous theories about the origins of a person's sexual orientation, but some believe that "sexual orientation is most likely the result of a complex interaction of environmental, cognitive and biological factors", and that genetic factors, play a "significant role" in determining a person's sexuality. The APA currently officially states that sexual orientation is not chosen and cannot be changed, a radical reversal from the recent past, when non-normative sexuality was considered a deviancy or mental ailment treatable through institutionalization or other radical means.
The term "straight" is an ordinary (nontechnical) English word used to describe a heterosexual person, although the term appears to have originally derived from mid-20th century gay slang, ultimately coming from the phrase "to go straight" (as in "straight and narrow"), or stop being gay . One of the first uses of the word in this way was in 1941 by author G. W. Henry. Henry's book concerned conversations with homosexual males and used this term in connection with the reference to ex-gays. Though not originally intended to refer to heterosexuals, like the meanings of many words, its primary usage has changed over time.
The term breeder, a word which is normally applied to non-human animals, is sometimes used as an offensive slur to describe heterosexuals.
- "Heterosexualism". HyperDictionary.com, Webnox Corp. (Cited February 13, 2004)
- Wikholm, Andrew, "Words: Heterosexual". Gay History.com. (Cited February 14, 2004)
- "Straight, Ex-gay". Descriptors for Sexual Minorities. The Hitchhiker's Guide to the Galaxy, H2G2. BBC. (Cited February 14, 2004)
- "Answers to Your Questions About Sexual Orientation and Homosexuality" American Psychiatric Association. (Cited February 9, 2004)
- "Heterosexual Sex". World Sex Explorer. (Cited February 14, 2004)
- Katz, Jonathan Ned (1995) The Invention of Heterosexuality. NY, NY: Dutton (Penguin Books). ISBN 0525938451.
- Human sexuality : Sex, Homosexuality, Bisexuality, Asexuality, Lifestyle, Sexual morality, Sexual norm, Situational sexual behavior, Sexual revolution, Sex-positive, History of heterosexuality, queer theory, queer studies, gender studies, heteronormativity
- Marriage : Bridegroom, Bride, Erotophobia
- Other : Heterosexism, Reparative therapy, Ex-gay, Gender and sexuality studies, Cruising for sex, Group sex, Ménage à trois, Masculism, Dating game show, Monogamy, Infidelity
- Lists: List of Isms, List of lifestyles, List of sexology topics
- Prevalence of heterosexuality
- Causes of sexual orientation
- Kinsey, Alfred C., et al., "Sexual Behavior in the Human Male". Indiana University Press. ISBN 0253334128
- Kinsey, Alfred C., et al., "Sexual Behavior in the Human Female". Indiana University Press. ISBN 025333411X
- "IOHR". International Organization of Heterosexual Rights.
- "Confidential Heterosexuality". Heterosexual Experience Stories. Raw Psychology Productions.
- "Straight Pride Wear". Straight Pride.com.
- "Straight Pride USA". Straight Pride USA.com.
- Keel, Robert O., "Heterosexual Deviance". (Goode, 1994, chapter 8, and Chapter 9, 6th edition, 2001.) Sociology of Deviant Behavior: FS 2003, University of Missouri - St. Louis.
- "Heterosexual partner rights raise questions". The News' View, Yale Daily News Publishing Company. January 27, 2004.
- Coleman, Thomas F., "What's Wrong with Excluding Heterosexual Couples from Domestic Partner Benefits Programs?". Unmarried America, American Association for Single People.