Maqalid al-'ulum (Keys to the Sciences) is a significant source on definitions of Arabic scientific terms in the post-classical period. Composed by an anonymous author, it contains over eighteen hundred definitions in the realm of twenty-one religious, literary, and rational sciences. The work was dedicated to the Muzaffarid Shah Shuja', who ruled over Shiraz and its neighbouring regions from 759/1358 to 786/1384. The present volume contains a critical edition of Maqalid al-'ulum based on its three extant manuscripts. In the introduction, the editors review previous scholarship on the text, present an overview of patronage at the court of Shah Shuja' and identify some of the sources used by the author of the work. They suggest that the work in its structure mirrors Abu 'Abdullah Khwarazmi's Mafatih al-'ulum, completed in 366/976.