This history is designed to present a dynamic approach to the study of ancient and medieval philosophy. It correlates ancient, medieval and modern ideas and shows the perennial significance of the contributions of ancient thinkers. To some extent this work is a re-evaluation of ancient philosophy. Thus, more space than is usual is devoted to the Skeptics and Philo, who have been very much underrated by earlier historians of philosophy. Philosophy, like many other field, is often dominated by convention and tradition. Hence many historians have followed blindly in the footsteps of Gomperz, Zeller, Burnet and Robin, who all had a tendency to underestimate the contributions of post Aristotelian philosophy.