The magmatic diversity of the Trans-Mexican Volcanic Belt is directly or indirectly controlled by two independent oceanic plates with differing geophysical and compositional parameters; by an extensional tectonic regime that operates with different intensities over the upper plate; by a continental basement with a diversity of ages, thick nesses, and compositions; and by a compositionally heterogeneous mantle wedge that has been modified to various extents by the slab-derived chemical agents. The convergent margin and the magmatic arc have not remained static throughout their geologic histories, but instead have shown significant changes in position, geometry, and composition. For these reasons, the Trans-Mexican Volcanic Belt is the result of one of the most complex convergent margins on the planet, the subject of more than a century of scientific investigations, and at the core of the most notorious debates on Mexican geology.