Adult adoption is a form of adoption between 2 or more adults in order to transfer inheritance rights and/or filiation. Adult adoption may be done for various reasons including: to establish intestate inheritance rights; to formalize a step-parent/step-child relationship or a foster parent/foster child relationship; or to restore the original legal relationship between adult adoptees and their natural families.
In Japan, adult adoption may be used in order to facilitate the continuance of a family business. This form of adoption is known as mukoyōshi (“son-in-law adoption”). Adult adoption may also be used in some jurisdictions by same-sex couples in order to establish inheritance rights.
Depending on the laws of the jurisdiction, adult adoption may not be available as a legal option. In the United Kingdom, only children may be adopted. The Adoption and Children Act (2002) states, "An application for an adoption order may only be made if the person to be adopted has not attained the age of 18 years on the date of the application."
In places where adult adoptions exist, it may or may not transfer filiation in addition to inheritance rights. For example, in Colorado, one can adopt an adult of age 21 or older for inheritance purposes, but filiation will remain unaffected. However, adoption of a person between the ages of 18 and 20 (inclusive) transfers both inheritance rights and filiation. 
- Ratliff, S. (2011). "Adult Adoption: Intestate Succession and Class Gifts under the Uniform Probate Code," (PDF). Northwestern University Law Review. 105 (4).
- Healing Families Dismembered By Adoption.
- Mehrotra, Vikas; Morck, Randall; Shim, Jungwook; Wiwattanakantangd, Yupana (2013). "Adoptive Expectations: Rising Sons in Japanese Family Firms" (PDF). Journal of Financial Economics. 108 (3): 840–854. doi:10.1016/j.jfineco.2013.01.011. ISSN 0304-405X.
- "Keeping it in the family: Family firms adopt an unusual approach to remain competitive". The Economist. December 1, 2012. Retrieved 10 September 2015.
- Jacobs, Deborah L. (May 20, 2009). "Adult Adoption a High-Stakes Means to an Inheritance". New York Times. p. Your Money, Estate Planning.
- "Adoption and Children Act 2002". legislation.gov.uk. Section 49 (4).
- "Article 1 Adoption - Adults, Section 14-1-101 "Adoption of Adults"" (PDF). Domestic Matters (PDF)
|url=(help). Colorado Revised Statutes. Title 14. p. 1.
- "Article 5 Relinquishment and Adoption, Part 2 Adoption, Section 19-5-201 "Who May be Adopted"" (PDF). Children’s Code. Colorado Revised Statutes. Title 19. p. 301.
- Family Formation Law Adopt an Adult
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