The origin of the world has always been a topic for scientific inquiry. This lecture examines some approaches to this question from the Middle Ages. Although the creation by God of the world out of nothing was an undoubted article of faith, medieval natural philosophers strove to understand the natural causes at work in creation and how God organized his creation. In this lecture we examine the fascinating Hexameral literature, commentaries on the first chapters of Genesis, used by medieval thinkers for investigations into natural philosophy.