In general, the distinction between passive and active euthanasia is based on the idea that in forms of passive euthanasia, the death of the person receiving euthanasia is caused by an omission (letting die), while in forms of active euthanasia, death is caused by an action (killing). Proponents of this distinction emphasize that in the former case, the death of a patient is not caused by the actions of medical professionals, but by another cause. Death is therefore not caused by the killing of a third person, but, for example, by the discontinuation or refusal of treatment.

Others argue instead that the distinction between active and passive euthanasia is based on the differentiation between ordinary and extraordinary measures. Ordinary measures and means are those that relate to medications or treatment methods that are readily available and can be used without causing severe pain, costs, or other inconveniences, but which give those affected a reasonable hope of improvement in their health. Extraordinary measures or means are those that relate to medications or treatment methods that cannot be used without causing severe pain, costs, or other inconveniences, but which, if used, do not give the person concerned reasonable hope of an appropriate health benefit. While refraining from ordinary measures is always morally impermissible, the provision of extraordinary measures is not morally required because there is no obligation to prolong human life under all circumstances.

As these briefly outlined differentiations already show, there is no consensus among proponents as to what in detail distinguishes passive from active euthanasia. It is also disputed by many that this is in fact a morally relevant difference. (cf. Quante, 1998; Rachels, 1989; McMahan 2002, pp. 457–462; Hillebrand, 2009, pp. 113f.).