Abstract: The hydrogen gas component of the interstellar medium (ISM) makes up ~75% of the overall mass fraction and exists over a myriad of phases: a cold molecular phase that fuels star formation, a thermally bi-stable neutral phase (HI), and an ionized phase (HII) around regions of massive star formation. The lifecycle of the hydrogen gas in the ISM is a fundamental driver of galaxy evolution; however, many questions remain open about the interplay between these different phases. For instance, how does the turbulent warm neutral medium imprint itself on the cold neutral and molecular phases to influence subsequent star formation? I will present observations of HI emission and absorption that, when analyzed in conjunction, trace the important phase transition between the cold and warm components of the ISM. These observational data come from an assortment of novel surveys: the Galactic ASKAP survey (GASKAP-HI), which provides the most sensitive and spatially resolved view of our own Milky Way and nearby Magellanic Clouds, and the Local Group L Band Survey (LGLBS) that extends this view to members of the Local Group, including the Milky Way analogue M31. In particular, we observe the presence of cold HI into the circumgalactic medium of the Milky Way that is embedded within a turbulent warm component. These unprecedented observations probe the physical state of HI over a large range of environments and will provide touchstone HI data sets for the Magellanic System, Milky Way, and Local Group for the coming decade.