This paper analyzes of some aspects of Hans Kelsen’s life and activities during his stay in the USA. It focuses on his legal and philosophical thought which, although Kelsen was required to take into account the ideas of American and Anglo-Saxon empiricism within his own writings, remained largely unchanged compared to that previously elaborated by him in Europe. In particular, the paper analyzes the concepts of justice developed by Kelsen in English in several essays during his stay in the United States, which were published in 1957 in an important book, What is Justice? Justice, Law and Politics in the Mirror of Science. The paper considers the two aspects of justice developed by Kelsen. One aspect is a strong legal aspect of justice, which forms part of the structure of the Reine Rechtslehre and is fully consistent with Kelsen’s theory. The second aspect elaborated is a broader concept of justice,—it is the philosophical aspect, which is extremely profound and complex, and is rooted in his culture,—along with his philosophical and human Weltanschauung. It refers mostly to secular religions, to the archaic aspects of human beliefs, to myth and to the primitive conception of the soul. Even though they may be completely different, the two concepts go hand in hand, and one does not prevail over the other. However, Kelsen more deeply and significantly develops the philosophical and cultural concept of justice, and for this reason that aspect of Kelsen’s concept of justice is of greater interest.