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

The most commonly used method of suicide varies between countries, and is partly related to the availability of effective means. Common methods include hanging, pesticide poisoning, and firearms. Suicide resulted in 828,000 deaths globally in 2015 (up from 712,000 deaths in 1990). This makes it the 10th leading cause of death worldwide.

Approximately 0.5% to 1.4% of people die by suicide, about 12 per 100,000 persons per year. Three quarters of suicides globally occur in the developing world. Rates of completed suicides are generally higher in men than in women, ranging from 1.5 times as much in the developing world to 3.5 times in the developed world. Suicide is generally most common among those over the age of 70; however, in certain countries those aged between 15 and 30 are at highest risk. There are an estimated 10 to 20 million non-fatal attempted suicides every year. Non-fatal suicide attempts may lead to injury and long-term disabilities. In the Western world, attempts are more common in young people and females.

Views on suicide have been influenced by broad existential themes such as religion, honor, and the meaning of life.The Abrahamic religions traditionally consider suicide an offense towards God due to the belief in the sanctity of life. During the samurai era in Japan, a form of suicide known as seppuku (harakiri) was respected as a means of making up for failure or as a form of protest.Sati, a practice outlawed by the British Raj, expected the Indian widow to kill herself on her husband's funeral fire, either willingly or under pressure from the family and society. Suicide and attempted suicide, while previously illegal, are no longer so in most Western countries. It remains a criminal offense in many countries. In the 20th and 21st centuries, suicide has been used on rare occasions as a form of protest, and kamikaze and suicide bombings have been used as a military or terrorist tactic