This chapter reports on the epidemiology of suicidal behaviors in each type of mood disorder, discusses the boundaries between sadness and depressive disorders in relation to suicide, and highlights possible prevention strategies for suicide in patients with mood disorders. Mood disorders are a leading public health problem worldwide. They are not only enormously detrimental to society and the economy and have negative consequences on personal and interpersonal circumstances, but are also related to the fatal outcome of suicide. Unipolar disorders primarily include major depressive disorder and dysthymic disorder. Bipolar disorder is characterized by alternating episodes of mania and depression over the course of life. While suicidal behaviors are convincingly predicted by clinical depression, their association with normal sadness has been neglected and never properly examined. This is likely the result of the confusion between normal sadness and depressive disorders among contemporary psychiatrists and researchers.