Suicidal ideation may be defined as any self-reported thoughts of engaging in suicide-related behavior. It is commonly considered the first step of the suicide process, before suicidal planning and suicidal act, the outcome of which may be fatal or not. Its lifetime prevalence ranges from 2.6% to 25.4% in the general population according to different countries, sex, and age groups and its relationship with suicidal planning ranges from 5% to 96%. This review chapter first aimed to provide a comprehensive definition of the concept of suicidal ideation together with providing related epidemiological data and then to review the major risk factors for suicide such as the positive history of previous suicide attempts, the association with psychiatric and physical conditions, low social support, and stressful life events. We also aimed to investigate the paths leading from ideation to suicidal acts providing some useful tools for the identification and evaluation of suicidal ideation in the clinical practice. Furthermore, the possible controversial role of early childhood experiences, abuse and neglect in the development of suicidal ideation will be explored. Finally, the impact of universal, selective, and indicated suicide prevention strategies in lowering suicide rates will be analyzed.