Suicide is a complex phenomenon that arises from the interaction of biological, social, and psychological risk factors and is considered a serious health problem worldwide. Recent research has revealed the complexity underlying the neurobiological mechanisms of suicide. In particular, genetic factors, dysfunction of the serotonergic system, hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, stress system, and lipid metabolism are implicated. Findings have highlighted the association between noradrenergic hyperactivity, abnormalities in glial cells, and signaling errors with suicidal behavior. Additionally, differences in cognitive functions have been observed in individuals who attempted suicide, and morphological changes in the frontolimbic network have been detected in brain neuroimaging studies. Identification of neurobiological risk factors can play a crucial role in preventing suicide and developing treatment strategies. This book chapter aims to examine the neurobiological basis of suicidal behavior.