  The hydrogen 21-cm signal is predicted to be the richest probe of the young
Universe including eras known as the cosmic Dark Ages, the Cosmic Dawn when the
first star and black hole formed, and the Epoch of Reionization. This signal
holds the key to deciphering processes that take place at the early stages of
cosmic history. In this opinion piece, we discuss the potential scientific
merit of lunar observations of the 21-cm signal and their advantages over more
affordable terrestrial efforts. The moon is a prime location for radio
cosmology which will enable precision observations of the low-frequency radio
sky. The uniqueness of such observations is that they will provide an
unparalleled opportunity to test cosmology and the nature of dark matter using
the Dark Ages 21-cm signal. No less enticing is the opportunity to obtain a
much clearer picture of Cosmic Dawn than what is achievable from the ground,
which will allow us to probe properties of the first stars and black holes.
