In the early 20th century, a political movement to secure access to euthanasia and assisted suicide began in the United States. The multitude of organizations associated with this effort has undergone an array of mergers, splits, and name changes, channeled through two progenitor organizations—the Euthanasia Society of America and the Hemlock Society. A few chronologies mapping the metamorphoses of these organizations are available, but they are not accessible in the medical literature. Moreover, they are not comprehensive, lack consistency, and are not rigorously validated. As debates about the legalization of euthanasia and assisted suicide continue, it is important to have a common understanding of the history behind these developments, including recognition of the factors driving these adaptations. In this paper, we offer a comprehensive and definitive history to aid those interested in knowing the roots of these organizations and those that are still active today.