This chapter provides a comprehensive, evidence-based examination of dilution ventilation as a primary engineering control for airborne infection prevention in the built environment. It integrates principles from fluid dynamics, building physics, microbiology, and epidemiology to explain how respiratory aerosols are generated, transported, diluted, and removed within indoor spaces. Moving beyond the seemingly outdated droplet–airborne dichotomy, the chapter situates respiratory transmission on a continuum and demonstrates why ventilation effectiveness, airflow patterns, and occupancy dynamics are as critical as nominal air change rates. The chapter critically evaluates dilution ventilation in comparison with complementary strategies including filtration, ultraviolet germicidal irradiation (UVGI), and emerging air-cleaning technologies, highlighting both their strengths and limitations. Through discussion of the Wells–Riley model, the concept of infectious quanta, and the rebreathed air fraction framework, it shows how ventilation rate (Q) exerts a mathematically and biologically meaningful influence on infection probability. Carbon dioxide (CO2) is presented as a practical proxy for ventilation adequacy and real-time risk management, while acknowledging its limitations in the presence of air cleaning, poor mixing, or variable occupancy. Empirical evidence from healthcare facilities, schools, public transport, and tuberculosis wards is used to connect theoretical models with observed transmission outcomes. The chapter also addresses the challenges posed by short-range airborne transmission, imperfect mixing, and ventilation failure modes, illustrating why compliant systems may still permit outbreaks. Energy, climate, and pollution trade-offs are examined, emphasizing the need for hybrid solutions such as energy recovery ventilation, demand-controlled filtration, and adaptive operational strategies. Ultimately, the chapter argues that dilution ventilation remains the backbone of infection-resilient building design, but must be intelligently combined with air cleaning, monitoring, and occupancy-aware control to be effective. By framing ventilation as a public health intervention rather than a comfort-only service, the chapter calls for a paradigm shift toward performance-based indoor air quality standards that prioritize human health, resilience, and transparency.