Interplanetary Coronal Mass Ejections (ICMEs) are formed of plasma and magnetic field launched from the Sun typically at faster speed than
the Solar Wind (SW).  These coherent magnetic structures, frequently formed by a flux rope, interact strongly with the SW.  Such interaction is
reviewed by comparing the results obtained from in situ observations and numerical simulations. Like fast ships in the sea, fast ICMEs drive an
extended shock in front.  However, their interaction with the SW is much more complex than that of the ship analogy.  For example, as they
expand in all directions while traveling away from the Sun, a sheath of SW plasma and magnetic field accumulates in front, which partially
reconnects with the ICME magnetic field. Furthermore, not only ICMEs have a profound impact on the heliosphere, but the type of SW
encountered by an ICME has an important impact on its evolution (e.g. increase of mass, global deceleration, lost of magnetic flux, distortion
of the configuration).