This chapter focuses on the prototypical public health emergency commonly referred to as complex humanitarian emergencies (CHEs). CHEs are confined within nation-state borders and result in massive numbers of internally displaced populations (IDPs). The humanitarian community relies on use of specific direct and indirect indices to assess consequences including severity of the conflict, measure the impact or outcome of interventions in declining mortality and morbidity, and identify the most vulnerable of populations requiring care. In CHEs, deaths from the complications of a simple and preventable childhood disease highlight the inherent threat to the immune system that results from malnutrition and micronutrient diseases. Immediate psychosocial interventions focus on supporting public health activities aimed at reducing mortality and morbidity, mitigating the burden on the community of managing the seriously mentally ill who need specialized psychiatric care, and mobilizing community-based resiliency and adaptation to new circumstances affecting people during the emergency.