Mercy killing, or euthanasia, is slightly different from assisted suicide. When we talk about mercy killing we usually mean voluntary euthanasia, where the patient has consented to die with assistance, usually from a doctor. This is legal, under certain conditions, in the Benelux countries (The Netherlands, Belgium and Luxembourg) although only The Netherlands has had much publicity. Assisted suicide, which can be seen as a form of euthanasia, is also legal in Switzerland; it has been legal for many years, but only became well known for the practice when people started travelling from other countries to lend their lives at a special clinic in Zurich.

Certain US states have also voted to allow assisted dying, again under specific conditions. At present the only states are Oregon, Montana and Washington. But it's under discussion in other states, and in fact several other countries, including the UK, are now debating the idea of a change in the law, so the list of countries that allow euthanasia may well be longer in a few years' time.