A trans man (short for transgender man) is a man who was assigned female at birth. Trans men have a male gender identity, and many trans men undergo medical and social transition to alter their appearance in a way that aligns with their gender identity or alleviates gender dysphoria.

The umbrella term trans is a shortening of both transgender and transsexual, and describes anyone whose gender identity does not align with their assigned sex. Trans men who transition are commonly referred to as female-to-male (FTM or F2M).

The term transsexual originated in the medical and psychological communities, and is generally considered a subset of transgender, although the two are not always interchangeable. It predominantly describes people with medically diagnosed gender dysphoria, and who desire to permanently transition to the opposite sex via sex reassignment therapy. Many trans people prefer the labels transgender or trans, considering them more inclusive and less stigmatizing. However, others, such as Buck Angel, reject the label of transgender. The GLAAD media reference guide advises against describing people as transsexual, except for individuals who explicitly identify as such.

Transmasculine (sometimes clipped to transmasc) is a broader term for all trans individuals with predominantly masculine identities or gender expression, and includes trans men as well as non-binary people who were assigned female at birth and may have an identity that is partially masculine but not entirely male.

The alternate spelling transman is sometimes used interchangeably. However, like transwoman, it is often associated with trans-exclusionary views which hold that trans men are distinct from men, and thus require a separate word to describe them. For this reason many transgender people find the spelling offensive.

Originally, the term trans men referred specifically to female-to-male transsexual people who underwent hormone replacement therapy (HRT) or sex reassignment surgery (SRS), or both. The definition of transition has broadened to include theories of psychological development or complementary methods of self-acceptance. Many of those who identify as transgender face gender dysphoria.

Transsexual and transgender men may seek medical interventions such as hormones and surgery to make their bodies as congruent as possible with their gender presentation. However, many transgender and transsexual men cannot afford or choose not to undergo surgery or hormone replacement therapy.

Many who have not undergone top surgery choose to bind their breasts. There are a few different methods of binding, including using sports bras and specially made binders (which can be vest-type, or wrap-around style). Tape or bandages are often depicted in popular culture.

Some trans men might also decide to pack, to create a phallic bulge in the crotch of clothing. However, this is not universal. Trans men who decide to pack may use anything from rolled up socks to specially made packers, which resemble a penis. Some packers are also created for trans men to be able to urinate through them (stand-to-pee, or STP, devices), or for sexual penetration or other sexual activity (known as "pack-and-play").

Transitioning might involve some or all of the following steps:

• Social transition: using a preferred name and pronouns, wearing clothing seen as gender appropriate, disclosure to family, friends and usually at the workplace/school.
• Sex reassignment therapy: hormone replacement therapy (HRT), and/or surgery (SRS)
• Legal affirmation: name and (sometimes) sex marker correction in legal identification documents.

Being socially accepted as male (sometimes known as passing) may be challenging for trans men who have not undergone HRT and/or surgery. Some trans men may choose to present as female in certain social situations (e.g. at work). After physical transition, trans men usually live full-time as male. However, some transmasculine individuals might choose to use and engage their bodies to be pregnant, birth a baby, and breastfeed.

In the United States, the ratio of trans men within the general population is unclear, but estimates range between 1:2,000 and 1:100,000. A U.S. Census Bureau study in 2015 suggests that there were around 58,000 name changes in census records consistent with female to male transitions although only 7,500 of these changed their sex coding as well.

In a study by Kara Devaney, entitled Transgender Research Literature Review, it is addressed that the term transgender encompasses a myriad of different and unique identities that do not follow the "normal" rules of gender. Miriam J. Abelson writes, "There is no question that trans men's experiences are men's experiences and give insight about men, masculinity, and gender inequality."

Like cisgender men, trans men can have any sexual orientation or sexual identity, including heterosexual, gay, bisexual, and queer, and some trans men consider conventional sexual orientation labels inadequate or inapplicable to them. The literature commonly indicates that sexual attraction to those of their same gender (e.g., trans men liking men and trans women liking women) is considerably less common among trans men than among trans women; the majority of trans men are reported as heterosexual. Surveys from the National Center for Transgender Equality show more variation in sexual orientation or sexual identity among trans men. In NCTE's 2015 Transgender Survey of respondents who identified as trans men, 23% identified as heterosexual or straight. The majority (65%) identified their sexual orientation or sexual identity as queer (24%), pansexual (17%), bisexual (12%), or gay/same-gender loving (12%).

Some trans men date heterosexual women, while other trans men date queer women; the latter might be because queer women are less invested in the gender and sexual anatomy of a person when it comes to selecting an intimate partner. It is also common for trans men to have histories with the lesbian community or to feel that they identify better with that community because of its wide acceptance of gender variance, with a number of trans men having previously identified as lesbian (often as a "butch lesbian") before realizing that they are instead transgender.

Trans men have less success integrating socially within cisgender gay men's communities, which tend to be more body-focused, especially in terms of being phallocentric. Yitzchak et al. state that, as a result, they more commonly see gay trans men partnering with each other than with cisgender gay men. There are, however, cases of women being likelier than men to thoroughly question trans men about their motivations for modifying their bodies.

Some scholars argue against assumptions that trans men are predominantly heterosexual and usually have lesbian histories. In scholars Dan Irving and Rupert Raj's book Trans Activism in Canada, researchers state, "There is still a common misperception that trans men are largely heterosexual amongst those who conflate gender identity and sexual orientation. It is frequently assumed that trans men are exclusively attracted to women and have lesbian histories prior to transition." They add, "Recent data from the Trans PULSE project (Bauer, Redman, Bradley, & Scheim, 2013) challenge this assumption, with 63 percent of female-to-male spectrum trans people in Ontario reporting non-heterosexual identities and/or past-year sex with trans or non-trans men." They also argue that, based on some research, "many non-trans gay men have welcomed trans men into gay communities and have increasingly recognized trans men as potential sexual and romantic partners."

Trans men and transmasculine people often face difficulty and discrimination receiving medical treatment, due to both bias against assigned-female patients and against transgender people. In the 2015 U.S. Transgender Survey, 42% of 8,037 trans men reported negative experiences with healthcare providers. There is a lack of credible research about how to provide adequate healthcare to transmasculine people undergoing medical transition, notably with doctors having difficulty diagnosing breast cancer in people who have undergone top surgery. HIV infection between trans men and others is still increasing.

Trans men with an intact female reproductive system may become pregnant. According to surveys compiled by Medicare for Australia, 75 male-identifying parents gave birth in Australia in 2016, and 40 in 2017. Although testosterone therapy eventually induces amenorrhea in most trans men, trans men with uteri are still at risk of pregnancy even if they no longer have periods. Additionally, trans men are likely to live in poverty and have inadequate access to healthcare, so many do not have access to the contraceptives they may want or need. Trans men can use barrier methods, oral contraceptives, IUDs, and other methods of contraception while taking testosterone.

Trans men must discontinue testosterone while attempting to conceive, while pregnant, and while breastfeeding, because high levels of testosterone during pregnancy can cause fetal abnormalities, specifically with the urogenital system of a female fetus.

Trans men experience issues during pregnancy not experienced by pregnant women. For example, trans men may experience discrimination on the base of their gender while receiving obstetric care. Many providers are unfamiliar with the needs of transgender patients. Additionally, some men report that being pregnant made their gender dysphoria worse.

Despite the 2020s restrictions on transgender children and adults participation in athletics, trans boys and men have competed in many individual and team sports at high school, college, and professional levels. Early known examples of trans men who competed at international levels were often competitors in women's championships, and came out as trans men later in life. They include Zdeněk Koubek, a Czech national champion and medal winner at the 1934 World Women's Athletic games in track; Willy De Bruyn, a Belgian cyclist who became unofficial women's world champion in 1934, born intersex and raised as a girl but later identified as a man; and French sprinter Pierre Brésolles, who ran the 100 metre and 200 metre races and won third place in the 100 meter dash in the Oslo European Championship in 1946. Later Olympic athletes include Andreas Krieger (b. 1965), a German former shot putter who competed on the women's East German athletics team at SC Dynamo Berlin, and Ricardo del Real, a Mexican taekwando competitor in the 2000 Summer Olympics.

More recently, Chris Mosier, a duathlon and triathlon competitor on the US National team in duathlon, successfully challenged the International Olympic Committee former policy that required surgery before transgender athletes could compete. Mosier's challenge led to the creation and adoption of new IOC guidelines for the participation of transgender athletes and in World Championships. Mosier was considered the catalyst for change in the policy in January 2016, after he successfully advocated for change in the policy Another Olympic team athlete, former member of Japan's Olympic fencing team Fumino Sugiyama, is now a transgender rights activist and works to promote acceptance and participation of trans athletes in Japanese sports.

Track and field athletes include retired German pole vaulter Balian Buschbaum and American NCAA college athlete Keelin Godsey (hammer throw). Competitive athletes in individual sports include American professional boxer Patricio Manuel, and Japanese former professional boxer Shindo Go, who held the World Boxing Council women's flyweight title from 2013 to 2014; NCAA swimmer Schuyler Bailar, and high school state wrestling champion Mack Beggs, who won the Texas state girls' wrestling title in 2017 despite efforts to bar him from participating. (State rules required him to compete according to sex assigned at birth.)

In basketball, noted trans men include Jay Mulucha, an LGBTQI activist and Ugandan basketball player with the Magic Stormers in the Federation of Uganda Basketball League (FUBA), and American basketball player Kye Allums, the first openly transgender NCAA Division I college athlete. Harrison Browne was the first openly transgender athlete in professional American hockey, coming out in 2016 and transitioning medically after his retirement from professional sports in 2018. Kumi Yokoyama is a Japanese footballer who plays as a forward for Okayama Yunogo Belle and the Japan women's national team. Quince Mountain was the first transgender dog musher to compete in the Iditarod dogsledding race in 2020.

Transgender men can face discrimination as a result of their status as trans men. Such discrimination may include sexual violence.

• Trans woman
• List of transgender people
• List of transgender-related topics

• Becoming a Visible Man by Jamison Green
• Just Add Hormones: An Insider's Guide to the Transsexual Experience by Matt Kailey
• Transmen and FTMs: Identities, Bodies, Genders, and Sexualities by Jason Cromwell
• FTM: Female-to-Male Transsexuals in Society. by Aaron H. Devor
• Second Son: Transitioning Toward My Destiny, Love and Life by Ryan Sallans

• Medical Therapy and Health Maintenance for Transgender Men: A Guide For Health Care Providers free ebook, ISBN 0-9773250-0-8
• TransGuys.com A magazine for trans men
• FTM International An organization serving the female-to-male trans community.
• Original Plumbing magazine Quarterly magazine with online component focusing on culture and diversity in the trans male community.