What is Philosophy? is the text of a lecture delivered in the city Heidegger Norman Cerisy la Salle in 1955. The text revolves around the role philosophy can play in a society dominated by technology and constantly threatened by the risk of nuclear destruction of the planet. Therefore, we are at a conference that contains the essential elements of the author's mature thought, from the relentless criticism of the technique and the final course of philosophy, to the fragmentation of human identity, the gradual weakening of the values of humanism or the contributions of poetry. In line with Adorno, Horkheimer, Marcuse and Heidegger seeks an alternative to a type of instrumental domination in the form of a huge and complex technological gear has been imposed in many sectors of contemporary society. In this context raises the fundamental question of the role of philosophy. On the one hand, warn about the risks of this plot and, second, try to restore lost ties with nature and immediate reality. Only a serene and meditative attitude, an attitude characteristic of philosophy, allows individuals to break free from the bondage technique and think about the proximity of the things of everyday life. That is the way that Heidegger draws at this conference to return to that mysterious and ancient correspondence between being and man. The clarity of the text provides a first access to the basic ideas of the author and reflect on a problem that still has full force. Interest philosophers and philosophy students.