This book is the introductory manual to Marxism intended for students of social sciences. The reader will find here an exposition of the set of topics related to philosophy, sociology, economics and politics without failing to observe the unity that makes Marx's theory an irreducible totality. José Ferraro offers us a means to approach Marx and Engels directly and thinking on our own, without arbitrarily clouding or simplifying his thinking and without attempting to replace the direct reading of their texts. This didactic intention is congruent with the author's central thesis: Marx's humanism is not only an ethical position but a powerful instrument for scientific research and the result of a critical synthesis of Western philosophical thought. This work synthesizes long years of teaching and research experience and a prolonged effort to develop, disseminate and make critical thinking useful for the social struggles of our time. For this edition, some errors were corrected and some formal modifications were introduced that improve the exposition in some passages of the previous one.