Twelve Decades: Probing the Interstellar Medium from kiloparsec to sub-AU scales

After a decade of great progress in understanding gas flow into, out of, and through the Milky Way, we are poised to merge observations with simulations to build a comprehensive picture of the multi-scale magnetized interstellar medium. These insights will also be crucial to four bold initiatives in the 2020s: GWs, FRBs, cosmic B-mode, and the EHT.