This chapter contains sections titled: Introduction Antigen Entry via the Gastrointestinal Tract Peyer's Patches Mesenteric Lymph Node Dendritic Cells of the Lamina Propria Pathogens Target Intestinal Antigen Presenting Cells Antigen Entry via the Skin Systemic Dissemination of Antigens/Infectious Microorganisms Antigen Presenting Cells in the Liver Dendritic Cells Kupffer Cells Liver Sinusoidal Endothelial Cells Conclusion