Suicide is a leading cause of death worldwide and perhaps the most puzzling and devastating of all human behaviors. Suicide research has primarily been guided by verbal theories containing vague constructs and poorly specified relationships. We propose two fundamental changes required to move toward a mechanistic understanding of suicide. First, we must formalize theories of suicide, expressing them as mathematical or computational models. Second, we must conduct rigorous descriptive research, prioritizing direct observation and precise measurement of suicidal thoughts and behaviors and of the factors posited to cause them. Together, theory formalization and rigorous descriptive research will facilitate abductive theory construction and strong theory testing, thereby improving the understanding and prevention of suicide and related behaviors. Due to scientific advances, there have been significant declines in many once-leading causes of death over the past 100 years, yet global suicide rates have remained fairly stable for decades. The lack of progress in understanding, predicting, and preventing suicide is due in part to the limitations of current scientific theories of suicide.After providing a brief history of suicide theories, we argue that these theories are limited due to two fundamental factors: (i) they are imprecise, comprising vaguely defined components and underspecified relationships among those components, precluding concrete theory predictions that could be tested; and (ii) there is a lack of rigorous descriptive research that is necessary to inform the generation, testing, and development of more precise theories.We provide several guiding principles to address these limitations, focusing on the need to formalize theories as mathematical and computational models and to collect rigorous and intensive descriptive research on key suicidal outcomes and the factors posited to give rise to those outcomes.