自杀是指当事者蓄意使自己死亡的行为。试图自杀或非致命的自杀行为一般视为自残，有自杀的意图，但后来没有死亡。协助自杀是指一个人借由提供建议或是其他方式，协助有死亡意愿者达成目的，但没有直接参与导致死亡的过程，这和安乐死不同，在安乐死中他人有直接参与导致死亡的过程。自杀意念是指有自杀的意图。

自杀的风险因素包括忧郁症、躁郁症、思觉失调症、人格障碍或是物质滥用在内的心理疾病，其他因素还有因为经济问题、人际问题或是霸凌而有的压力而产生的冲动行为。以往曾试图自杀的人，再度自杀的可能性也较高。自杀防制的方式包括管制可能用来自杀的物品（如枪枝及毒药），提高取得的难度，治疗心理疾病及物质滥用，改善媒体报导自杀的方式，及提升经济条件等。生命线之类的协谈电话虽常见，但有关其成效的研究还不太充份。

Suicide is the act of intentionally causing one's own death. Risk factors include mental illness such as depression, bipolar disorder, schizophrenia, personality disorders, alcoholism, or drug abuse. Others are impulsive acts due to stress such as from financial difficulties, troubles with relationships, or bullying. Those who have previously attempted suicide are at high risk of future attempts. Suicide prevention efforts include limiting access to method of suicide such as firearms and poisons, treating mental illness and drug misuse, proper media reporting of suicide, and improving economic conditions. Although crisis hotlines are common, there is little evidence for their effectiveness.