This paper presents an analysis of the concept of Technik in Heidegger`s philosophy, especially of its relationship with Being and with man. It is divided into three sections: (1) Technik as a Mode of Unconcealment. Here the author shows that Technik is not a way of human making, it is instead a kind of the unconcealment of Being. But, what is the nature of this unconcealment? Section (2) shows that the nature of Technik is Gestell, a term that cannot be correctly translated into English. In Heidegger, Gestell is the collective noun of a group of "stellen", e. g. bestellen, umstellen, aufestellen, darstellen, sicherstellen, nachstellen and verstellen…etc. Section (3), its title is "The Relationship between Gestell and Man", interprets how the thinking of man is dominated and endangered by Gestell, and how man escapes its domination.