The preceding chapters in this primer have provided an overview of the immune response that serves as a background for understanding potential sites for immune modulation and immunotherapy. A number of soluble growth and activation factors are released from various cell populations involved in the immune response. They play vital roles in the initiation, propagation, and regulation of immunologic responses. Pharmacologic immunomodulators include suppressive and stimulatory agents. Immunosuppressive therapies include antimetabolites, cytotoxic drugs, radiation, adrenocortical glucocorticosteroids, immunophilins, and therapeutic antibodies. The field of clinical immunostimulation is emerging as an important therapeutic modality for a number of immunodeficiency diseases, chronic viral infections, and cancer. These compounds will be discussed in terms of general principles, molecular targets, major indications, and adverse effects.