Human immunology has advanced at a breakneck pace in recent years, and additional breakthroughs are expected in the near future. Although the immune system is incredibly complex, new tools and abilities are being developed to study it. The discovery of thousands of distinct monoclonal antibodies that allow the identification of a wide variety of cell subpopulations and the functional study of immune cells is one of the most important reasons in these breakthroughs. In various disorders, research into the interplay of the immune system with other systems, such as the neurological and endocrine systems, or the microbiome, has yielded intriguing insights with substantial clinical implications. All of these advancements can be used to a variety of immune-mediated diseases, but the recent success of several immunotherapies is revealing new approaches to study and influence the immune system for our benefit. The treatment of disease by activating or suppressing the immune system is known as immunotherapy or biological therapy. Immunotherapies that elicit or magnify an immunological response are called activation immunotherapies, while those that diminish or suppress the immune response are called suppression immunotherapies.