Euthanasia can be broadly defined as the ending of a patient's life at his or her request or out of feelings of mercy. The types are classified according to two main considerations: the degree of consent on the part of the patient and the way in which the procedure is carried out. Euthanasia can be voluntary, non-voluntary or involuntary, and it can be an active or passive procedure. Many legal systems in the world treat all forms as criminal homicide. There are, however, some places where the legality depends on its type.
When euthanasia occurs at the explicit request of a patient, it is referred to as voluntary euthanasia. A few governments have rendered this form legal or, if not completely legal, it has been decriminalized. In some countries, voluntary euthanasia is classified as homicide, but if a doctor can satisfy certain legal requirements, it is not considered criminal homicide, and he or she will not be prosecuted. In other places, physician-assisted suicide is not classified as euthanasia, and doctors are not prosecuted if the procedure is carried out as stipulated.
Non-voluntary euthanasia is when a person is unable to give his or her consent to the procedure, such as when he or she is unconscious, comatose or legally incompetent. It is also referred to as non-voluntary when a person has previously expressed his or her wish to die under specific circumstances but cannot at that moment speak for himself or herself. Children generally are perceived as legally incompetent — for example, children cannot sign legal contracts — and this logic applies in the case of euthanasia as well. Child euthanasia is internationally held to be illegal in almost all cases, although some places might specify particular circumstances in which it is permitted.
Non-voluntary euthanasia is sometimes erroneously confused with involuntary euthanasia, which is distinct. The term non-voluntary signifies that the act is carried out without the patient’s consent, and involuntary means that it is done against the patient’s expressed will. "Slippery slope" arguments are often made against all forms on the supposition that legalizing one form of it might someday lead to cases of involuntary euthanasia.
In terms of procedural distinctions, there are two types: active and passive. Active euthanasia implies actions being taken to end another’s life, such as a lethal substance being administered. Passive euthanasia occurs when life-saving actions or treatments are willingly withheld. In many parts of the United States and other countries, it is legally acceptable for a doctor to acquiesce to a patient’s request to cease the use of life-sustaining treatments.