The concept of a "legal sex" is complex, though for simplicity the term will be used in this discussion. The World Professional Association for Transgender Health advocates a simple administrative procedure to change legal identity documents to match experienced gender. While self-determination of legal gender is the law in a small (but growing) number of countries, including Argentina, Denmark, Malta, and Ireland, most countries require the involvement of health professionals, if legal "change of sex" is possible at all.
Under United States federal law, and in some states, surgery is not required to change legal sex, but a health professional must certify that their patient has undergone "necessary" medical or psychological treatment for transition. In completing this paperwork, the health professional should be aware that there is no particular clinical treatment (such as hormones or surgery) that is "necessary" for all trans people, and that legal documents reflecting a sex congruent with one's gender identity contribute to a patient's health, by supporting employment, safe travel, and other necessities of daily living, as well as facilitating access to medical care.
In some jurisdictions, there is a surgical requirement to change legal sex. The health provider may have leeway, depending on the law, as there is no particular surgery that is "necessary" for all trans people. Some trans people are unable to change their birth certificate in their home state or country, but may still change their gender markers on their U.S. passport, Social Security card, and driver's license.
Transgender people may encounter a conflict between their legal sex and sex-specific medical care, such as screening for cervical cancer or prostatic disease. While state laws may vary, in some cases it may be necessary for the provider to contact the insurance company and explain the specific circumstances in the case of a sex-specific denial. Once legal documents have been changed, patients should be sure to update their legal name and sex with their insurance company and medical provider to prevent a denial based on a mismatch of information.
Legal change of name is not a gendered process in many, but not all jurisdictions; in most jurisdictions the name change process for transgender people is identical to that for non-transgender people.
- U.S. Department of State guidelines for passports 
- U.S. Social Security Administration guidelines 
The National Center for Transgender Equality maintains a resource center with links to guidelines for changing identification documents in each U.S. state .
Information on changing gender identity documents in Europe can be found at TGEU: Transgender Europe.
- WPATH Public Policy Committee, Green J. WPATH Statement on Legal Recognition of Gender Identity .2015 [cited 2016 Mar 24].
- The Open Society Foundations, Byrne J. License to be Yourself: Laws and advocacy for legal gender recognition of trans people. New York, NY; 2014 May [cited 2016 Mar 24].
- National Center for Transgender Equality. ID Documents Center. National Center for Transgender Equality. 2016 [cited 2016 Mar 24].
- Lambda Legal.Resources for Changing Your Documents. Lambda Legal: Know Your Rights. [cited 2016 Mar 24].
- U.S. Department of State; Bureau of Consular Affairs. Gender Transition Applicants. U.S. Passports and International Travel. [cited 2016 Mar 24].
- U.S. Social Security Administration. Program Operations Manual System (POMS): RM 10212.200 - Changing Numident Data for Reasons other than Name Change. Official Social Security Website. 2013 [cited 2016 Mar 24].
- (TGEU) Transgender Europe. [cited 2016 Mar 24].