Studies of the faint spectral distortions in the CMB are emerging as the next frontier in experimental research. There are three general types of primordial spectral distortions that are predicted by theory: (i) chemical potential mu-type distortions, (ii) Compton y-type distortions, and (iii) a recombination line signal. The mu-type distortions are the result of particles interacting with photons during the very early universe when photons were in equilibrium with matter (z > 50,000). The y-type distortions are produced later (z < 50,000) when Compton scattering becomes an inefficient mechanism for energy exchange; this is the same mechanism that produces the thermal Sunyaev-Zel’dovich effect in galaxy clusters. A recombination line spectrum should have been produced when hydrogen and helium nuclei in the primordial plasma captured electrons during recombination, producing emission lines distinctly different from the usual CMB blackbody spectrum (1000 < z < 10,000). The recombination line signal today should span the GHz to THz range of the electromagnetic spectrum. Although this emission line signal is faint when compared with the CMB blackbody spectrum, the distinct spectral features are, in principle, detectable. A detection of this signal would be a direct confirmation of the recombination history of the Universe because these emission lines must exist if our understanding of the early Universe is correct, and a precise characterization of the spectrum will yield information about the relative abundances of hydrogen and helium in the Universe during recombination because these two nuclei produce unique features in the spectrum.