The resilience of our immune system is remarkable. It is always on guard against various pathogens that we encounter whether we eat, work, or sleep. A healthy body needs a balanced immune system to combat a variety of disease-causing agents. More importantly, the harmonious cross-talk between the immune system and other systems of our body is the key to good health. When this multi-level system fails us, we become prone not only to germs and diseases but also to many autoimmune disorders and cancers. Immunomodulators are substances that assist in the proper functioning of the immune system directly or indirectly by turning down some proteins (immune suppressors) or turning up others (immune enhancers). Among different classes of immunomodulators, cytokines play an important role as messenger molecules that effectively connect different processes and regulate immune cell growth and their maturation and responsiveness. They are the group of small glycosylated polypeptides with molecular mass less than 30 kDa and are key mediators in innate and adaptive immunity, hematopoiesis, inflammation, tumorigenesis, viral pathogenesis, etc. The chapter here deals with cytokines and their action as immunomodulators at different levels of the immune system of our body and their role in immunotherapies.