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  Since the Universe was filled with hydrogen atoms at early times, the
most promising method for observing the epoch of the first stars is to
measure the hyperfine line of hydrogen at a wavelength of 21 cm. Such
an observation of the "cosmic dawn" era was considered speculative
when I helped lay out the theoretical predictions a decade ago, but
there is now an enormous, promising observational effort (in which I
am involved within the Square Kilometre Array). There is also an
important aspect of early cosmic history that can potentially be
probed today. The difference between the early evolution of the
baryons and the dark matter should imprint a specific signature that
can be probed via galaxy surveys. We have recently attempted the first
such measurement; detecting this would provide a novel confirmation of
the standard cosmological model.