A legal guardian is a person who has the legal authority (and the corresponding duty) to care for the personal and property interests of another person, called a ward. Usually, a person has the status of guardian because the ward is incapable of caring for their own interests due to infancy, incapacity, or disability. Most countries and states have laws that provide that the parents of a minor child are the legal guardians of that child, and that the parents can designate who shall become the child's legal guardian in the event of their death.

Courts generally have the power to appoint a guardian for an individual in need of special protection. A guardian with responsibility for both the personal well-being and the financial interests of the ward is a general guardian. A person may also be appointed as a special guardian, having limited powers over the interests of the ward. A special guardian may, for example, be given the legal right to determine the disposition of the ward's property without being given any authority over the ward's person. A guardian appointed to represent the interests of a person with respect to a single action in litigation is a guardian ad litem.

A guardian is a fiduciary and is held to a very high standard of care in exercising his powers. If the ward owns substantial property the guardian may be required to give a surety bond to protect the ward in the event that dishonesty or incompetence on his part causes financial loss to the ward.