[Presented at HWO25 "Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology"] Understanding how galaxies form and evolve over the 13.8-billion-year history of the Universe is one of the ultimate goals of modern astronomy. The Habitable Worlds Observatory (HWO), with its unprecedented sensitivity and spatial resolution, will enable transformative science in the study of galaxy formation and evolution. In this talk, I will highlight key science cases that HWO will help advance—such as chemical enrichment, gas inflows and outflows, and the growth of supermassive black holes—toward a comprehensive understanding of the galactic ecosystem.