The historical concept and definition of sexual orientation varies and has changed greatly over time; for example the word "gay" was not used to describe sexual orientation until the mid 20th century.
 A number of different classification schemes have been used to describe sexual orientation since the mid-19th century, and scholars have often defined the term "sexual orientation" in divergent ways.
 Indeed, several studies have found that much of the research about sexual orientation has failed to define the term at all, making it difficult to reconcile the results of different studies.
 However, most definitions include a psychological component (such as the direction of an individual's erotic desire) and/or a behavioural component (which focuses on the sex of the individual's sexual partner/s).
 Some prefer to simply follow an individual's self-definition or identity.
Scales of sexual orientation are classification schemes of different sexual orientations. Definitions of the term "sexual orientation" normally include two components: the "psychological" and the "behavioral" component, but the definitions of the two components vary between researchers and across time.
 Those difficulties motivate researchers to define scales to measure and describe sexual orientation.
 Most sexual behavior and sexual orientation scales are motivated by the view that sexual orientation is a continuum.
 The Kinsey scale works from a continuum viewpoint and is the most prevalent sexual orientation scale.
Justinus Soni "Justin" Fashanu ( ; 19 February 1961 – 2 May 1998) was an English footballer who played for a variety of clubs between 1978 and 1997.
 He was known by his early clubs to be gay, and came out to the press later in his career, becoming the first professional footballer to be openly gay.
 He was also the first black footballer to command a £1million transfer fee, with his transfer from Norwich City to Nottingham Forest in 1981, but had little success as a player afterwards, although he continued to play at senior level until 1994.
This is a list of LGBT characters in modern written fiction.
 The historical concept and definition of sexual orientation varies and has changed greatly over time; for example the word "gay" wasn't used to describe sexual orientation until the mid 20th century.
 A number of different classification schemes have been used to describe sexual orientation since the mid-19th century, and scholars have often defined the term 'sexual orientation' in divergent ways.
 Indeed, several studies have found that much of the research about sexual orientation has failed to define the term at all, making it difficult to reconcile the results of different studies.
 However, most definitions include a psychological component (such as the direction of an individual's erotic desire) and/or a behavioral component (which focuses on the sex of the individual's sexual partner/s).
 Some prefer to simply follow an individual's self-definition or identity.
 See homosexuality and bisexuality for criteria that have traditionally denoted lesbian, gay and bisexual (LGB) people.
Gay, Straight, and the Reason Why: The Science of Sexual Orientation (2010; second edition 2016) is a book about the development of sexual orientation by the neuroscientist Simon LeVay, in which the author argues that sexual orientation is an aspect of gender that emerges from the prenatal sexual differentiation of the brain, and criticizes Freudian and behaviorist explanations of sexual orientation.
 "Gay, Straight, and the Reason Why" received numerous positive reviews, praising it for LeVay's wide-ranging overview of scientific research on sexual orientation, but the book also received some mixed or negative reviews, criticizing it on grounds such as LeVay's willingness to rely on studies with inadequate sample sizes.
 In 2012, "Gay, Straight, and the Reason Why" received the Bullough Book Award for the most distinguished book written for the professional sexological community published in a given year.
Sexual fluidity is one or more changes in sexuality or sexual identity (sometimes known as sexual orientation identity).
 There is significant debate over whether sexuality is stable throughout life or is fluid and malleable.
 Scientific consensus is that sexual orientation, unlike sexual orientation identity, is not a choice.
 While scientists generally believe that sexual orientation is usually stable (unlikely to change), sexual identity can change throughout an individual's life, and may or may not align with biological sex, sexual behavior or actual sexual orientation.
<ref name="Concordance/discordance in SO"> </ref> There is no consensus on the exact cause of developing a sexual orientation, but genetic, hormonal, social and cultural influences have been examined.
 Scientists believe that it is caused by a complex interplay of genetic, hormonal, and environmental influences.
Ego-dystonic sexual orientation is an ego-dystonic mental disorder characterized by having a sexual orientation or an attraction that is at odds with one's idealized self-image, causing anxiety and a desire to change one's orientation or become more comfortable with one's sexual orientation.
 It describes not innate sexual orientation itself, but a conflict between the sexual orientation one wishes to have and the sexual orientation one actually possesses.
Robert Hampton "Robbie" Rogers III (born May 12, 1987) is an American professional soccer player who plays for LA Galaxy in Major League Soccer.
 He plays as a winger and as a left back.
 Rogers has also represented the United States men's national soccer team.
 In February 2013, Rogers came out as gay, becoming the second male soccer player in Britain to do so after Justin Fashanu in 1990.
 On May 26, 2013, he became the first openly gay man to compete in a top North American professional sports league when he played his first match for the Galaxy.
Sexual identity is how one thinks of oneself in terms of to whom one is romantically or sexually attracted.
 "Sexual identity" may also refer to sexual orientation identity, which is when people identify or dis-identify with a sexual orientation or choose not to identify with a sexual orientation.
 Sexual identity and sexual behavior are closely related to sexual orientation, but they are distinguished, with "identity" referring to an individual's conception of themselves, "behavior" referring to actual sexual acts performed by the individual, and "sexual orientation" referring to romantic or sexual attractions toward persons of the opposite sex or gender, the same sex or gender, to both sexes or more than one gender, or to no one.
The historical concept and definition of sexual orientation varies and has changed greatly over time; for example the word "gay" was not used to describe sexual orientation until the mid 20th century.
 A number of different classification schemes have been used to describe sexual orientation since the mid-19th century, and scholars have often defined the term "sexual orientation" in divergent ways.
 Indeed, several studies have found that much of the research about sexual orientation has failed to define the term at all, making it difficult to reconcile the results of different studies.
 However, most definitions include a psychological component (such as the direction of an individual's erotic desire) and/or a behavioural component (which focuses on the sex of the individual's sexual partner/s).
 Some prefer to simply follow an individual's self-definition or identity.

Question: Though separate nationalities, soccer players Robbie Rogers and Justin Fashanu shared which common sexual orientation?
Answer: openly gay