安乐死（希腊语：Ευθανασία；英语：euthanasia；eu意为「好」，thanatos衍生自死神塔那托斯），有「好的死亡」或者「无痛苦的死亡」的含意；但此名称与实际作法不断地受到争议。这是一种给予患有不治之症的人以无痛楚、或更严谨而言「尽其量减小痛楚地」致死的行为或措施，一般用于在个别患者出现了无法医治的长期显性病症，因病情到了晚期或不治之症，对病人造成极大的负担，不愿再受病痛折磨而采取的了结生命的措施，经过医生和病人双方同意后进行，为减轻痛苦而进行的提前死亡。批评者认为此行为有「杀人」或「协助自杀」的嫌疑。被安乐死是指在未经病人自身同意的情况下，由其亲属向医生申请或医生主观判断实行安乐死。

Euthanasia (from Greek:εὐθανασία; "good death": εὖ, eu; "well" or "good" – θάνατος, thanatos; "death") is the practice of intentionally ending a life in order to relieve pain and suffering.

There are different euthanasia laws in each country. The British House of Lords Select Committee on Medical Ethics defines euthanasia as "a deliberate intervention undertaken with the express intention of ending a life, to relieve intractable suffering". In the Netherlands and Flanders, euthanasia is understood as "termination of life by a doctor at the request of a patient".