The results of a combined spectroscopic and computational study of lanthanide hydrides with the general formula MHx(H2)y, where M = La, Ce, Pr, Nd, Sm, Eu, and Gd, x = 1−4, and y = 0−6 are reported. To understand the nature of the dihydrogen complexes formed with lanthanide metal hydride molecules, we have first identified the binary MHx species formed in the ablation/deposition process and then analyzed the dihydrogen supercomplexes, MHx(H2)y. Our investigation shows that the trihydrides bind dihydrogen more weakly than the dihydrides and that the interaction between the central lanthanide and the H2 molecules occurs via a 6s electron transfer from the lanthanide to the H2 molecules. Evidence is also presented for the SmH and EuH diatomic molecules and the tetrahydride anions in solid hydrogen.