Hydrogen is adsorbed on metal surfaces either molecularly or atomically. Due to the light mass, hydrogen has a large zero-point vibrational energy and an extended feature of its nuclear wavefunction. The zero-point motion affects the hydrogen adsorption site and the wavefunction is possibly delocalized over the surface. Because of the nuclear spin, on the other hand, molecular hydrogen is classified into ortho and para species, that have different rotational quantum numbers. The ortho and para species have different adsorption energy and undergo ortho-para conversion through magnetic interaction with metal surfaces.