Everyone who dies by suicide has thought about suicide prior to their action. Suicidal ideation is, therefore, one of the most important risk factors for suicide. This book explores and illustrates current research on this risk factor. There are reviews of selected aspects of suicidal ideation. Karolina Krysinska and David Lester review research on whether religiosity is a protective factor for suicidal ideation, while John Gunn reviews whether bullying is a risk factor. Cathy Pederson reviews research on suicidal ideation in the chronically ill. Three research studies are presented: Mahboubeh Dadfar on mattering as a protective factor in Iranian psychiatric patients, Jenny Huen and her colleagues on correlations of suicidal ideation in Chinese students, and Steven Stack on suicidal ideation in men who have been raped. The content of suicidal ideation is discussed by James Overholser and his colleagues, and Jennifer Laffier presents examples of suicidal communications in social media. Finally, Frank Bailey presents two case studies of individuals in which their suicidal ideation is presented in the context of their life histories. The chapters illustrate the importance and the complexity of suicidal ideation and its role in leading to suicidal actions.