[en] At the beginning of the universe the fundamental forces of the standard model (the electro-magnetic interaction, the weak and strong nuclear interactions) are supposed to be unified because it was the domain of very high energy. When the universe cooled down the symmetry associated to this unique interaction broke generating topological defects called cosmic strings. Cosmic strings have nothing to do with the string theory. Cosmic strings form a cosmological network that evolve with time, cosmic strings moving at the speed of light. Simulations have shown that cosmic strings have a 10^-30 m long characteristic radius and a linear density of about 10²¹ kg/m. Because of the high value of the linear density, cosmic strings could be detected via gravitational effects like the deviation of light rays or the detection of specific gravitational waves. Detection attempts have been made in the past 2 years but no cosmic string has been detected so far. (A.C.)