A legal guardian is a person who has been appointed by a court or otherwise has the legal authority (and the corresponding duty) to make decisions relevant to the personal and property interests of another person who is deemed incompetent, called a ward. For example, a legal guardian might be granted the authority to make decisions regarding a ward's housing or medical care or manage the ward's finances. Guardianship is most appropriate when an alleged ward is functionally incapacitated, meaning they have a lagging skill critical to performing certain tasks, such as making important life decisions. Guardianship intends to serve as a safeguard to protect the ward.

Anyone can petition for a guardianship hearing if they believe another individual cannot make rational decisions on their own behalf. In a guardianship hearing, a judge ultimately decides whether guardianship is appropriate and, if so, will appoint a guardian. Guardians are typically used in four situations: guardianship for an incapacitated senior (due to old age or infirmity), guardianship for a minor, and guardianship for developmentally disabled adults and for adults found to be incompetent. A family member is most commonly appointed guardian, though a professional guardian or public trustee may be appointed if a suitable family member is not available.