More than half a century of groundbreaking discoveries in the field of immunology have been made, and no cells have shown more potential than the lymphocytes known as T cells. These little miracles play a crucial role in protecting us from infectious diseases and cancer, as well as predisposing us to certain diseases, such as autoimmunity, when they are dysfunctional or dysregulated. This book aims to foster collaboration between world-class bench scientists and clinicians in the fields of immunology, pathology, and oncology as they come together to highlight the complexity and diversity of T cells as well as their contributions to our immune homeostasis and overall health and to discuss the revolutionary therapeutic applications of T cells in fighting infectious diseases, autoimmunity, and malignant neoplasms.