Macrophages are widely distributed innate immune cells, which play a pivotal role not only in the primary response to pathogens but also in adaptive immune response, in tissue repair and in the maintenance of local tissue homeostasis. This book includes current research in the life cycle, functions and diseases associated with macrophages. Topics discussed include macrophages as regulatory and effector cells in the immune system; macrophages from human pluripotent stem cells; mucosal macrophage phenotype and functionality in homeostasis and pathology; macrophage plasticity and polarization; defective macrophage function in Crohn’s disease; macrophages in viral infection and atherosclerosis; and macrophage polarization in the course and treatment of autoimmune diseases.