The great characteristic of postmodern societies is to live as if God did not exist. In old Europe, our times are times of practical atheism. Indeed, a good part of Western society has settled into the forgetfulness of God. But: does it really matter if God exists or not? It is essential, if we want a critical and constructive dialogue, to understand what atheism is like and what its roots and arguments are. Be clear about its origin and its motives, the historical evolution and the current causes of this great mass phenomenon. This book therefore seeks to shed light on the essence of current atheism to facilitate a sincere and fruitful dialogue between those who affirm the existence of God and those who deny it.