Ellery Stowell's detailed study of humanitarian intervention, published in 1921, rewards a close reading today. In this article, I consider two broad themes of his work that continue to be of particular relevance. First, his discussion of the rightfulness of humanitarian intervention is grounded in a concept of responsible sovereignty which is remarkably similar to present-day notions of "sovereignty as responsibility" and "the responsibility to protect." I suggest that this points to an enduring intimate relationship between sovereignty and responsibility which both advocates and critics of intervention for the protection of populations today have a problematic tendency to either ignore or forget. Second, his argument that external actors possess not merely a right but an obligation to intervene to enforce the protection of populations has clear parallels with the present-day notion that the society of states bears a "responsibility to protect" populations. I observe that, while much has changed, advocates of "the responsibility to protect" continue to struggle to overcome some of the same dilemmas about the "imperfect" nature of this obligation that confronted Stowell.