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Transitioning is the process of changing one's gender presentation and/or sex characteristics to accord with one's internal sense of gender identity – the idea of what it means to be a man or a woman, or genderqueer (in-between). For genderqueer people, their internal sense of gender identity is neither solely female nor male. For transgender and transsexual people, this process commonly involves reassignment therapy (which may include hormone replacement therapy and sex reassignment surgery), with their gender identity being opposite that of their birth-assigned sex and gender. Transitioning might involve medical treatment, but it does not always involve it. Cross-dressers, drag queens, and drag kings tend not to transition, since their variant gender presentations are (usually) only adopted temporarily.
Transition must begin with a personal decision to transition, prompted by the feeling that one's gender identity does not match the sex that one was assigned at birth. One of the most significant parts of transitioning for many transgender people is coming out for the first time. Transitioning is a process, not an event, that can take anywhere between several months and several years. Some people, especially genderqueer people, may spend their whole life transitioning as they redefine and re-interpret their gender as time passes. Transitioning generally begins where the person feels comfortable: for some, this begins with their family with whom they are intimate and reaches to friends later or may begin with friends first and family later. Sometimes transitioning is at different levels between different spheres of life. For example, someone may transition far with family and friends before even coming out at work.
Transitioning is sometimes confused with sex reassignment surgery (SRS), but that is only one possible element of transitioning. Many people who transition choose not to have SRS, or do not have the means to do so. Whereas SRS is a surgical procedure, transitioning is more holistic and usually includes physical, psychological, social, and emotional changes. Some transgender and non-binary people have little or no desire to undergo surgery to change their body but will transition in other ways.
Passing refers to being perceived and accepted by other people in a manner consistent with one's own gender identity. This can be one aspect of transitioning, though genderqueer people may choose to purposely not pass. Someone observing, for example, a trans woman passing may know of her trans status but still consider her a woman, but sometimes they might not know about her trans status.
Going full-time refers to a person living one's everyday life as the gender one identifies with. One's passing can be limited by safety, legal or bodily restraints. For instance, someone who has worked at a job as female may feel they cannot safely present as male and may switch jobs instead. Mental health professionals who go by the World Professional Association for Transgender Health (WPATH) Standards of Care for the Health of Transsexual, Transgender, and Gender Nonconforming People do not normally require a patient to go full-time for at least a year (a period of time generally referred to as the "Real-Life Experience" or "Real-Life Test", but mental health professionals who do not adhere to these guidelines do, before recommending surgery.
Going stealth means to live as a gender without other people realising a person is transgender. Trans people often go stealth in public but not with family, partners, or intimate friends. There have been many cases of people who have lived and worked as a gender identity different from their gender assigned at birth. See Category:Transgender and transsexual people for some examples.
A social transition is a transition that only involves social, cosmetic, and legal changes, without any medical interventions. People who socially transition may ask others to refer to them by their preferred name and pronouns, and some may legally change their name. 
Detransitioning is the process of changing one's gender presentation and/or sex characteristics back to accord with one's assigned sex. Detransitioning has also been called retransitioning, though retransitioning can also mean transitioning again after detransitioning.
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Transitioning is a complicated process that involves any or all of the gendered aspects of a person's life. Below are some common parts of transitioning. People may choose elements based on their own gender identity, body image, personality, finances, and sometimes the attitudes of others. A degree of experimentation is used to know what changes best fit them. Transitioning also varies between cultures and subcultures according to differences in the societies' views of gender.
- Social, psychological, and aesthetic aspects
- Coming out
- Gender role changes
- Socially choosing a new name or nickname to be referred to by
- Asking others to use a set of pronouns different from before; for example, a trans man would ask to be referred to as he rather than she, or a genderqueer/non-binary person might ask to be referred to as they or by a pronoun like ze
- Personal relationships take on different dynamics in accordance with gender
- Altering objects and clothing worn to better represent gender identity
- Adopting new grooming or makeup techniques
- Having one's hair styled differently
- Adopting mannerisms consistent with the new gender role
- Adopting a new sexual role and/or performing new sexual acts, especially if the body's sex organs have changed
- A person's ideas about gender in general may change which may affect their religious, philosophical and/or political beliefs
- Legal aspects
- Legally changing their name to something consistent with their gender identity
- Having one's legal sex marker changed on documents such as driver licenses, birth certificates, passports, and in the US, Social Security cards
- In some countries, being exempted from the military draft for MTF individuals, or being required to register for it for FTM individuals.
- Physical aspects
- Brown, M. L. & Rounsley, C. A. (1996) True Selves: Understanding Transsexualism – For Families, Friends, Coworkers, and Helping Professionals Jossey-Bass: San Francisco ISBN 0-7879-6702-5
- K. Auer, Matthias (October 2014). "Transgender Transitioning and Change of Self-Reported Sexual Orientation". PLOS.
- World Professional Association for Transgender Health (September 2011). "Standards of Care for the Health of Transsexual, Transgender, and Gender Nonconforming People, Seventh Version" (PDF). http://www.tssurgeryguide.com/gender-therapists.html
- "Detransitioning: Going From Male To Female To Male Again". Vocativ. 15 June 2015. Retrieved 1 September 2017.
- "Transitioning Back To One's Assigned Sex At Birth". The TransAdvocate. 7 August 2013. Retrieved 1 September 2017.
- Elliot, Patricia (1 October 2008). "Book Review: Sally Hines, Transforming Gender: Transgender Practices of Identity, Intimacy and Care. Bristol: The Policy Press,2007.227 pp.ISBN 978-1-86134-9170 £24.99 (pbk).ISBN 978-1-86134-9163 £60.00 (hbk)". Sexualities. 11 (5): 646–648. doi:10.1177/13634607080110050603 – via SAGE Journals.
- Jerry J. Bigner, Joseph L. Wetchler, Handbook of LGBT-affirmative Couple and Family Therapy (2012, ISBN 0415883598), page 207: "gender transition can be achieved through the use of clothing, hairstyle, preferred name and pronouns, ..."
- "Sie Hir, Now: Terms for Gender Variant People". Archived from the original on May 13, 2012. Retrieved 2012-05-13.