Title: Characterizing the Multiphase Interstellar Medium in the Milky Way and Beyond Abstract: The composition of the interstellar medium (ISM) is dominated by hydrogen which exists over several thermal phases: a cold molecular phase (H2) that fuels star formation, a cold and warm atomic neutral phase (CNM and WNM, respectively) that coexists at the same pressure (HI), and an ionized phase (HII) found around areas of recent star formation. The lifecycle and interplay between these different thermal phases are fundamental drivers of galaxy evolution, though many questions regarding the physics behind the transitions between these phases remain open. For instance, how does the WNM-to-CNM fraction vary over a wide range of environments (e.g., metallicity and regions with strong local stellar feedback)? And how do these gradients affect the transition to H2 to fuel future star formation? In this talk, I will present recent science highlights from observations of HI emission and absorption from two novel surveys: the Galactic ASKAP survey (GASKAP-HI) being carried out on the Australian SKA Pathfinder, which provides the most sensitive and spatially resolved view of the atomic gas in our own Milky Way and nearby Magellanic Clouds, and the Local Group L Band Survey (LGLBS), performed with the Karl G. Jansky Very Large Array, that extends this view to prominent members of the Local Group, including the Milky Way analogue M31. These unprecedented observations probe the physical state of HI over a wide range of environments to provide touchstone data sets for the Magellanic System, Milky Way, and Local Group for the coming decade.