21-cm cosmology: from dark matter to the dark ages

The coming confrontation of 21-cm theory and observations will reveal to us new chapters in the history of the Universe. One of them is the cosmic dawn, a cosmic epoch with unique conditions, and thus potential for new discoveries. Another is the dark ages, which could become a powerful new probe of fundamental cosmology. Upcoming experiments, from Earth to the moon, can help determine the composition of the Universe and probe the properties of dark matter.