The interlinkages between environmental degradation, human health, and animal well-being are increasingly evident in the age of pandemics and climate disruptions. Environmental, One-Health & Planetary Health addresses these complex relationships, advocating for systems-based thinking that unites ecology, medicine, and public policy. Zoonotic disease emergence, antimicrobial resistance, and vector-borne infections are directly tied to land-use change, biodiversity loss, and pollution. Researchers are now advancing integrated surveillance systems, transdisciplinary risk models, and early intervention strategies that bridge human-animal-environment interfaces. The conceptual convergence of Environmental, One-Health & Planetary Health is driving novel frameworks for sustainable development that protect ecological and physiological integrity alike. Investment in cross-sector collaboration—from agriculture and veterinary science to urban planning and climate policy—is essential to building planetary health futures.