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 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. For genderqueer people, it is neither solely female nor male. 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.