Observing the 21cm line promises new ways to probe the Universe. Low-redshift observations of the cosmic structure will tell us about the nature of dark energy, whereas high-redshift observations of the Epoch of Reionisation will
tell us about the first luminous sources. This technique still contains challenges, the largest being contamination from astrophysical sources in our
own galaxy and beyond.
I will overview recent progress in probing these eras in the radio-band, and give a practical introduction to why novel interferometers are the future. I will also introduce a new method for the foreground cleaning, analysis, and
forecasting of such experiments. This method is both robust to significant uncertainty in the foreground structure, and statistically explicit about the information loss associated with the foreground removal.