This book takes the reader on a journey through past and current research on the Major Histocompatibility Complex (MHC/HLA). It describes how it was discovered, what its biological function is and its application in medicine. The reader will learn about the molecular structure of the encoded molecules and different aspects of their role in medicine, including organ transplantation, their link to autoimmune diseases, cancer immunity, resistance to infectious diseases, and other related scientific areas, such as population genetics. In particular, the book focusses on the impact of MHC/HLA altered expression in tumours and their relevance in cancer immune escape and immunotherapy. It contains a large number of original figures and photographs of pioneers in the field, who made seminal contributions. Each chapter is supported by relevant key publications and enriched with a personal account of the early research that has contributed to our current understanding of the role of the major histocompatibility complex. This book is an excellent resource for all scientists in the biomedical life sciences who wish to gain insight into the discovery of the MHC/HLA and the role of this important genetic complex in health and disease.