Euthanasia is generally classified as either "active" or "passive", and as either "voluntary" or "involuntary". Similar to euthanasia is "assisted suicide".

"Passive euthanasia" is usually defined as withdrawing medical treatment with the deliberate intention of causing the patient's death. For example, if a patient requires kidney dialysis to survive, and the doctors disconnect the dialysis machine, the patient will presumably die fairly soon. Perhaps the classic example of passive euthanasia is a "do not resuscitate order". Normally if a patient has a heart attack or similar sudden interruption in life functions, medical staff will attempt to revive them. If they make no such effort but simply stand and watch as the patient dies, this is passive euthanasia.

"Active euthanasia" is taking specific steps to cause the patient's death, such as injecting the patient with poison. In practice, this is usually an overdose of pain-killers or sleeping pills.