Massive stars can provide valuable information on a Galactic, extragalactic, and even cosmological scale. The radiative signatures observed in HII regions and star-forming galaxies are determined by massive stellar populations. Long-duration gamma-ray bursts, produced during the core-collapse deaths of unusual massive stars, can be utilized as powerful probes of the high-redshift universe. Finally, massive star populations in the Milky Way and Local Group allow us to closely examine how these stars evolve, how their physical parameters are impacted by host environments, and how they contribute to interstellar and intergalactic enrichment through processes such as nucleosynthesis, mass loss, and supernova feedback. I will present my latest research on the next generation of current stellar population synthesis models, detailed studies of gamma-ray burst host galaxies, and the impact of host environments on the physical properties and evolution of the Local Group massive star population. Combining examinations of distant star-forming galaxies and gamma-ray bursts with the study of nearby stellar populations in this manner will greatly improve our understanding of massive stars and their utility as tools that can directly contribute to our greater picture of the cosmos.