Archival letters have long been valued resources for historians, literary scholars, genealogists, and more, but letters from centuries past can hold information beyond that of their written contents. Before envelopes became widespread in the nineteenth century, letters were intricately folded in such a way that they became their own envelopes, often with security features to stave off prying eyes, a practice which has been termed "letterlocking" by modern researchers. Here, interested readers can learn about letterlocking by a team of interdisciplinary scholars dedicated to researching this historical practice. The home page provides an overview of their research, along with several photos and a short introductory video. For those interested in demonstrations, the categories section offers an extensive library of videos showing different styles and security levels of letterlocking, while the Dictionary of Letterlocking (DoLL) section offers a frequently illustrated catalog of terminology for those interested in letterlocking research. The letterlocking categories and the DoLL are works in progress with forthcoming updates as work on the project continues. The Unlocking History team is led by Jana Dambrogio, a conservator at MIT Libraries; and Daniel Starza Smith, a lecturer in Early Modern English Literature at King's College London.