The activity of Origen of Alexandria (185-253), one of the most prolific early Christian scholars, encompassed different branches of theology. His enormous exegetical achievement is grounded on solid philological and hermeneutical foundations. With his De principiis, the Alexandrian thinker was the creator of systematic theology, and in his Contra Celsum, he composed the most intellectual piece of Greek patristic apology. A common element of these different segments of activity is that they are based on scientific and logical principles and were developed with methodological consciousness. The main topic of this book is what Origen said in his writings about logic, rationality in its broadest sense, dialectic, and theory of science, and what the characteristics of his strategy of argumentation are.