Hot gas plays a vital role in shaping galaxy formation and evolution. However, even though we live in a disk galaxy, we know very little about the distribution of this hot gas, and how it impacts the disk galaxy evolution via the so-called “circumgalactic medium”. In this talk, I will discuss several outstanding questions in this field, including problems such as the “missing galactic baryons” and “missing stellar feedback”. I will also discuss how addressing these questions can help understand galaxy formation and evolution processes in general, as well as the baryonic matter distribution in the universe.