There are several kinds of power of attorney (POA), and they vary with the type and the extent of the authority that is being passed to the agent on the principal's behalf.

In springing power of attorney, the principal cannot, in writing or verbally, make the request that someone act as his power of attorney. The principal is declared to be not capable of thinking for himself, and therefore will need an attorney-in-fact. This declaration of incapacity is usually given by the principal's doctor, when the patient's health suddenly deteriorates as a result of a devastating accident, or in mental illness. In this kind of POA, care should be taken that all the necessary paperwork be properly signed and addressed, so that the principal's agent can actually help on the principal's behalf.

In a durable POA, the agent will act for the principal during his disability, the duration of which will be determined by the principal's doctor. In these situations, the agent will generally deal with financial and other transactions outlined in the POA documents.

In a limited POA, the acts that can be carried out by an agent is described, the time limit and the specified situations the agent can act on behalf of the principal. This POA will be revoked should the principal becomes incapacitated or dies.

In a general POA, the powers given the agent to perform on the behalf of the principal are total in nature and scope. This POA can only be revoked by death of the principal or by another deed.

A durable financial POA gives the agent authority to perform financial transactions on the principal's behalf only when he is not able to do so. This will include such things as managing property, the payment of bills, taxation and other financial issues.

In a healthcare POA and living wills, the agent will step in if the principal cannot give instructions regarding his health care and who should treat him when needed. The agent would be the one to make those decisions.

A living will is a type of POA that outlines the actions of medical personal if the principal's death is imminent , and relates to such things as life support. The principal could himself revoke the POA and override the agent's decisions, since he is still in control of his senses.