A primary factor in the development of caries is the presence of a host. A number of host-related subfactors can influence the caries process. These include tooth structure, the physical, chemical, and antibacterial properties of the saliva that surrounds the tooth, and the immunity conferred by the immunoglobulins in the host environment, the mouth. Understanding tooth anatomy and the composition of all the tooth tissues, the protective role of saliva, and the two main different types of immune responses by secretory Immunoglobulin A and Immunoglobulin G will help dental professionals reduce caries risk in their patients.