Euthanasia is usually defined as mercy killing, although assisted suicide often falls under the same laws. Mercy killing has a negative connotation; the major difference is whether the euthanized person still has the mental faculties to approve the death and either participate or sign off on it. It is usually divided into Voluntary (consent of patient), Non-Voluntary (patient cannot consent), and Involuntary (patient refuses consent).
In the United States, euthanasia is classified as Criminal Homicide and is punishable by the same standards as any other homicide, although cases can be individually argued in court and may receive lesser charges under extenuating circumstances. Euthanasia -- as mercy killing -- is illegal in all 50 states, while Physician Assisted Suicide/Dying (PAD) is legal in Washington, Montana, and Oregon.
Euthanasia in itself does not compromise an individual's freedom of choice, since the act is illegal unless it is passive. Freedom of choice only extends to illegal acts when we understand the consequences; most people say that they would not commit an illegal act unless they could get away with it, and therefore the freedom is to not act. However, PAD does directly involve the patient's choice, and so the illegality of PAD means that a patient who wants to end his own suffering is denied that as a choice.
PAD has gained increasing support around the world as methods of dying become more painless, and proponents argue that the choice to die is preferable than the non-choice to continue living in suffering. Legislation is in constant debate about the moral and ethical stances behind both euthanasia and PAD, and the legalization of PAD in three states means that Euthanasia may soon be reexamined as a viable choice.