Emerging and re-emerging infections arise when pathogens adapt, jump species, or exploit ecological and social change. This book explores drivers such as land use change, globalization, antimicrobial resistance, and climate shifts, and explains how surveillance, early detection, and rapid response can blunt their impact. It integrates One Health perspectives on zoonoses, diagnostic and genomic tools for pathogen discovery, and frameworks for outbreak investigation and risk communication. Chapters on vaccine development, therapeutics, and policy approaches emphasize preparedness and resilient health systems. Aimed at researchers, public-health planners, and policymakers, it combines theory with case examples to inform practical readiness efforts.