Launch of clinical investigation represents a substantial escalation in commitment to a particular clinical translation trajectory; it also exposes human subjects to poorly understood interventions. Despite these high stakes, there is little to guide decision-makers on the scientific and ethical evaluation of early phase trials. In this article, we review policies and consensus statements on human protections, drug regulation, and research design surrounding trial launch, and conclude that decision-making is largely left to the discretion of research teams and sponsors. We then review what is currently understood about how research teams exercise this discretion, and close by laying out a research agenda for characterizing the way investigators, sponsors, and reviewers approach decision-making in early phase research.