Abstract：Cosmic dawn marked the transformation of the universe from its hot initial state to today's complex universe of stars, planets, and life. The earliest stars, though, formed in small galaxies that are too far away for us to see directly. Instead, the most promising probe of these stars is the 21-cm absorption from the surrounding hydrogen. The first detection of the 21-cm signal from cosmic dawn was reported in 2018 by the EDGES experiment. The signal had a much larger amplitude than expected, presenting a puzzle. I realized that this can be explained by a novel property of dark matter. I have also been exploring an alternative explanation, of an enhanced radio background from early galaxies. More generally, I have been studying new ideas for analyzing maps of the 21-cm intensity using the cumulative distribution function.