The Church is an institution desired and created by Jesus Christ, who is the Word of God the Father embodied for the salvation of man. It is an alive and extensive reality that has its own structure and a history which interpenetrates with the history of humanity. The 2nd Vatican Council tried to propose to the contemporary world different images of the Church, which remains the mystical body of Christ. The Church, being a creation of Christ and being permanently animated by the Holy Ghost, cannot be destroyed neither by the humans, nor by the powers of darkness. The dogmatic constitution about the Church Lumen gentium is the outcome of many discussions that took place many years before the Council, discussions that were perpetuated until the emergence of this extensive document. This article is a detailed presentation of this document that represents the identity card of the Church, summoned to come upon the real needs of today man.