In this work the most characteristic and original of the philosophic thought of Martin Buber is shown in a clear and documented way. Especially, it deals with the transcendental exposition of the problem of the understanding of the other, with all its richness and autonomy, together with its circumstantial limitations. The thread of the exposition is the intent to describe positively the understanding that focuses on the essence, far beyond the object. Buber insists that the ego is not what defines the subject in a fundamental way-that is, the principle of its freedom, of its identity and its dignity as person-, neither it is self-consciousness in its Hegelian sense or transcendental consciousness in its Husserlian sense, but the personal core of one being. In contrast with the individualistic and collectivist conceptions of the human being, it stands out how vigorously this philosopher forms his vision of the human being as a person totally open and dialogical, and it is to underline his decision of placing his plenitude in the meeting and in the essential relation with the others. In this way, the philosophy of Buber is a philosophy of the alterity that feeds on the polemical dynamism of a radical and strong criticism of the anthology on which the Western culture has been basing until now. The else is not already, for the ego, simply one object that establishes a relation of objectification and use, but one "you " as someone else different as "me" who I meet and with whom I achieve my own being. In the cases that the subject perceives the other as an object, there is not reciprocity as basis of the responsibility in the ethic sense of the term. Diego Sánchez Meca is professor of History of Contemporary Philosophy at UNED. He is preoccupied with issues of German philosophy of the nineteenth and twentieth century, with special interest in authors such as Goethe, Schlegel, Schopenhauer, Nietzsche, Heidegger and Gadamer. Among his publications, are worthy of note: En torno al Superhombre, Nietzsche y la Crisis de la Modernidad (1989), Metamorfosis y Confines de la Individualidad (1995) y La Historia de la Filosofia como Hermenéutica (1996). This book is of interest for teachers and students engaged in philosophy, but likewise for the general public who is interested in philosophic works.