This chapter provides a detailed analysis of the Operation of mixed-mode ventilation during epidemics, concentrating on the pivotal role of Indoor Air Quality (IAQ). It underlines the importance of ventilation and pressure intake in IAQ management, particularly for airborne infection control. We explore Singapore and international ventilation standards, laying emphasis on various Ventilation strategies. However, our principal focus is mixed-mode ventilation, a combined approach of natural and mechanical methods, which we highlight as a promising and potentially energy-saving solution for IAQ management and airborne disease control. Our examination includes multiple case studies in diverse environments, such as a negative-pressure isolation ward, a residential master bedroom, and an office building, each evaluated through different methods, including computational fluid dynamics and experimental approaches. Our observations illustrate the significant role of efficient ventilation in improving IAQ, mitigating airborne infection risks, and enhancing occupant comfort, especially during epidemics.