Langstroth's place as the founder of modern beekeeping is so well established that any new information on his contribution to the development of the movable-frame hive is to be welcomed. The authors of this article have been able to study the notes Langstroth made in preparation for the fourth edition of his book, which was never published. These notes, and other material quoted, provide evidence which puts into rather a new perspective events which, a century ago, determined the course of world beekeeping since then.