This book by the American researcher S. Frederick Starr examines two of the most prominent figures in Arab-Islamic civilization during its heyday: Ibn Sina and Al-Biruni. It presents a portrait of their era and an analysis of their works within the context of a thesis that highlights the great contributions of human knowledge—additions, in the author's view, that could have been even greater had it not been for the circumstances leading to the decline of the civilization to which he belongs. The author's analysis of the works of the two great thinkers and scholars is based on extensive knowledge of these works, making the book rich in the knowledge it offers the reader in general. However, analyzing and evaluating the works in the context of the era in which they were produced, and in terms of the impact they left, also enriches specialists in philosophy and science in general. This translation of the book seeks to enrich the Arabic library, with notes and comments by the translator seeking to clarify aspects of it that are of particular interest to the Arab reader.