Stars form from dense molecular clouds that collapse under their own gravity, but most of interstellar space is filled with diffuse, unbound clouds of atomic gas. How do these turn into the denser clouds from which stars form? The critical intermediate stage is cold atomic gas, which can be mapped across the Galaxy with the 21cm hyperfine line of neutral atomic hydrogen. Cold gas shows up clearly as 21cm absorption shadows against warmer background line emission, much as cold dust couds appear as optical shadows against the starlight of the Milky Way. Many of the darkest hydrogen shadow clouds are concentrated in spiral arms, and they show a partial association with denser molecular gas, implying that this critical ingredient for star formation is still condensing. This work requires large, high-resolution surveys with telescopes like Arecibo and the Very Large Array, as well as numerical models to aid interpretation of the observations. In addition to radio surveys, optical images of dust mixed with the hydrogen gas can reveal turbulent energy cascades occurring within these clouds via angular power spectra. I will present recent results from my research, future plans, and ideas for student participation at WKU.