[4] A person, known as the grantor or donor in different jurisdictions, can only create a power of attorney if they have the requisite mental capacity.

Depending on the jurisdiction, a power of attorney may be oral and, whether witnessed, will hold up in court, the same as if it were in writing.

This means, for example, that if a principal authorizes someone to sell the principal's house or other real property, and the law requires a contract for the sale of real property to be in writing (which is required under the Statute of Frauds in most U.S. jurisdictions), then the authorization for the other person to sign the sales contract and deed must be in writing too.

For a power of attorney to become a legally enforceable document, at a minimum it must be signed and dated by the principal.

Even when not required, having the document reviewed and signed (and often stamped) by a notary public may increase the likelihood of withstanding a legal challenge.

[8] If the attorney-in-fact is being paid to act on behalf of the principal, a contract for payment may be separate from the document granting power of attorney.

[11] If ever required, a durable power of attorney can be revoked or changed as long as the principal is still mentally competent to act.

This particular affidavit gives the attorney-in-fact the authority to make health-care decisions for the grantor, up to and including terminating care and life support.

As the result of privacy legislation in the U.S., medical doctors will often not reveal information relating to capacity of the principal unless the power of attorney specifically authorizes them to do so.

Standardized forms are available for various kinds of powers of attorney, and many organizations provide them for their clients, customers, patients, employees, or members.

However, the grantor should exercise caution when using a standardized POA form obtained from a source other than a lawyer because there is considerable variation in approved formats among the states.

Robert's Rules of Order notes that proxy voting involves granting a power of attorney.

[20][21] The attorney's authority can be limited or broad, and can take effect immediately or only in certain circumstances (such as the grantor becoming mentally incapable).

[22][23] One can make a power of attorney document oneself for free using a web tool created by Community Legal Education Ontario or have a lawyer do it.

If one doesn’t make a Power of Attorney, the government will not automatically step in if one can’t manage own affairs.

In these circumstances a family member has the right to make your health care decisions or apply to become your “guardian” of property.

The government, through the Office of the Public Guardian and Trustee (OPGT), acts only in situations where it is legally required and where no other suitable person is available, able and willing.

[23] In English law, applying in England and Wales, anyone with capacity can grant a power of attorney.

[26] Many of the provisions in American law, described in the sections above, use terminology having different meaning from both common British usage and from the terms used in the Mental Capacity Act 2005.

Examples are 'enduring power of attorney', 'advance directive', and 'notary public': in English law, these terms do not have the same meaning as they have in America.

During the coronavirus pandemic that started in 2019, England and Wales permitted documents such as wills to be witnessed via video link; however, a power of attorney still had to be signed by hand by all persons involved, in the right order, and witnessed directly, although possibly through a window or outdoors.

Notarial witnessing is mandatory if the power of attorney is made in order to enter into a contract to buy or sell an interest in land, as this has to be done on a public register.