This primary historical research project examines the concept of “unintended pregnancy” in social and cultural context, seeking to explain how such an intimate concept as pregnancy planning became one of the major goals of late 20th and early 21st century US public health. Though women have actively planned and prevented pregnancy since at least the 19th century, only in the 20th did pregnancy planning become a site for medical and public health intervention. This research project will delve more deeply into the history of this medicalization process, specifically interrogating the framing of unintended pregnancy as a public health problem. Through the use of primary historical documents including archived correspondence, academic publications, and existing oral histories, the research will trace the development of measures of pregnancy intention, beginning with the Indianapolis Study in 1941–42. The study will investigate questions including: Why did researchers begin to study pregnancy intention? How were measures developed, and how did they change over time? When did unintended pregnancy enter the public health lexicon, and how has its treatment changed over time? By placing unintended pregnancy in historical context, we can advance our understanding of pregnancy planning and how women, their health care providers, and government officials agreed and disagreed about its meaning. Knowing this history can improve our sensitivity to our own historical context, inform present-day measure development, and encourage useful and generative self-reflection as researchers, policy-makers, and clinicians.