The light we receive from celestial objects encodes information about the energetic processes that produce the radiation, enabling us to explore the underlying physics. By observing in the X-ray band, we can study some of the hottest material and most energetic processes in the Universe, including supernova explosions and remnants, the emission from material near black holes, and the hot, diffuse plasma thought to pervade the space between galaxies. Alas, through their energetic nature, X-rays are challenging to detect and precisely measure. Twenty years ago, Chandra and XMM-Newton opened a new imaging capability that finally matched what had been possible in the optical for decades, revolutionizing our understanding of the energetic Universe. Yet detailed X-ray spectroscopy has remained elusive. We are now poised on the brink of a new revolution, as X-ray instruments combining high sensitivity with exquisite energy resolution are on the horizon. I will discuss some the approved and proposed X-ray astronomy missions that will usher in this revolution, including XRISM, Arcus, Athena, and Lynx. In particular, I will discuss the technical progress that will make these observatories feasible, including some work being done at MIT, and the exciting and ground-breaking science they will tackle.