This text comprises several essays on ancient Greek philosophy, inspired, as Sir Karl Popper himself states in his preface, by two desires - first, to illustrate the thesis that all history is the history of problem situations and that in following this principle we may further our understanding of the Presocratics and other thinkers of the past; and second, to show the greatness of the early Greek philosophers, who gave Europe its philosophy, its science and its humanism. This collection of essays, published together for the first time, not only elucidates the complexity of ancient Greek thought, but also reveals Popper's engagement with Presocratic philosophy and the enlightenment he experienced in reading Parmenides. This collection also includes some pieces that have never before appeared in print. These writings on Greek science, philosophy and history demonstrate Popper's life-long fascination with and love for the Presocratic philosophers, in particular Parmenides, Xenophanes and Heraclitus.