Legal gender, or legal sex, is a sex or gender that is recognized under the law. Biological sex, sex reassignment and gender identity are used to determine legal gender. The details vary by jurisdiction. Legal gender identity is fundamental to many legal rights and obligations, including access to healthcare, work, and family relationships, as well as issues of personal identification and documentation. The complexities involved in determining legal gender, despite the seeming simplicity of the underlying principles, highlight the dynamic interaction between biological characteristics, self-identified gender identity, societal norms, and changing legal standards. Because of this, the study of legal gender is a complex field that is influenced by cultural, historical, and legal factors. As such, a thorough investigation is necessary to fully understand the subject's implications and breadth within a range of legal systems and societies.