This lecture from Yale's Essentials of Global Health course examines infectious diseases that are newly appearing or resurging worldwide, alongside the growing problem of antimicrobial resistance. The session covers the nature and burden of conditions such as HIV, tuberculosis, malaria, and neglected tropical diseases, tracing the determinants and risk factors that drive their spread and identifying which populations bear the greatest burden. It also addresses how drug resistance develops and spreads, and what cost-effective interventions have proven successful in controlling outbreaks and slowing resistance. Part of a broader course sequence that later turns to noncommunicable diseases and injuries, this segment keeps its focus tightly on communicable disease threats, framing them through the standard global health lens of burden, risk factors, and affected populations before turning to practical responses.