This fully revised and significantly expanded second edition examines sex and gender differences in the immune system's response to bacterial, viral, and parasitic infections. The volume discusses both common and distinct molecular mechanisms that mediate these differences and illustrates how responses to vaccines may differ between the sexes and in pregnant individuals. Special emphasis is placed on the interplay between hormones and the immune system in the pathogenesis of HIV, SARS-CoV-2, influenza, malaria, tuberculosis, and amebiasis. This second edition includes completely rewritten chapters as well as all new contents. This book is intended for researchers in academia and industry as well as clinicians in the fields of microbiology, immunology, and pharmacology. By expanding knowledge in sex and gender medicine as a basis for developing personalized treatment strategies, the book contributes to UN Sustainable Development Goals 3 (health and well-being) and 5 (gender equality).