This book focuses on the Th17 cells and their involvement in health processes and a wide specter of disorders related to Th17 cells. The book intends to provide the reader with a comprehensive overview of the current knowledge on the hot and controversial topics regarding Th17 cells. Th17 cells have been investigated intensively in recent years. These cells play an essential role not only in protective immunity but also contribute to chronic inflammation in many immune-mediated disorders. The role of IL-17 and Th17 in different pathways has changed several paradigms in immunology, especially those related to chronic inflammation. The existing concepts of immunopathologic mechanisms related to Th17 cells in various pathological processes in the organism have been confirmed by many studies. Furthermore, the number of conditions influenced by Th17 cells seems to be increasing. The book covers the role of Th17 cells in human health and pathological processes such as inflammation, autoimmunity, allergy, cancerogenesis, etc. The pathologies related to these lymphocytes are in the field of rheumatology (rheumatoid arthritis, spondyloarthropathies, systemic sclerosis), gastroenterology (inflammatory bowel disease, celiac disease, colorectal cancer, dermatology, allergy, neurology (multiple sclerosis), and respiratory medicine (allergic rhinitis, asthma, cystic fibrosis), in both children and adults. Special attention is paid to the controversial interaction between Th17 cells and T regulatory cells in autoimmunity and inflammation.