This special issue grew out of a small conference The Known & the Unknown: Exploring Twelfth-Century Philosophy, which was funded by the Carlsberg Foundation, hosted by the Saxo Institute, and held at the University of Copenhagen in April 2018. Its central topic was the many, mostly unexplored, commentaries on Aristotle, Boethius, and Porphyry that constitute the key textual evidence for a fascinating phenomenon that, although it played a pivotal role in the philosophical revival of Western Europe, remains frustratingly underexplored to this day: the logical schools of the twelfth century. The present introduction has two parts. In the first part, John Marenbon lays out the background to this special issue of Vivarium as a whole, explaining both what the philosophical project pursued by twelfth-century logicians was and how, and how far, the historical project of understanding it has progressed over the last two hundred years. In the second part, Heine Hansen briefly presents the issue and its contents.