"Lectures on the Geometry of Numbers" is a scholarly book based on the lectures given by Carl Ludwig Siegel during the academic year 1945-46 at New York University. At a time when there was little literature on this subject, this work provides a precise and detailed introduction to the geometry of numbers, inspired by Minkowski's original works. Siegel places great emphasis on accuracy in both the text and illustrations, without altering the structure and style of the original lectures. The book is of interest to both emerging and established mathematicians, uniquely combining elements of arithmetic, algebra, geometry, and analysis. It is characterized by its accessible readability and offers insights into the thinking of an extraordinary mind that embodies both precision and aesthetic charm.