In this chapter, Dr. Gleicher first examines how autoimmunity and pregnancy interrelate. In doing so, he equates the fetal semi-allograft to a mini renal transplant, and takes the reader on a journey of discovery, comparing allogenic organ transplants with pregnancy. He then tackles the preconception period, addressing the search for subclinical autoimmunity. The involvement of autoimmunity with implantation and early pregnancy syndromes follows, discussing in more detail the recently described “implantation rash” and explaining early pregnancy loss. The role of class II HLA compatibility is examined with rheumatoid arthritis as original example. Mid-pregnancy is examined, with attention to treatments of laboratory autoimmune abnormalities and autoimmune diseases. Late pregnancy is discussed as a final immune challenge to the maternal immune system due to large amounts of paternal antigens entering the maternal circulation. Microchimerism, consequence of bi-directional cellular traffic, is explained as essential for allograft tolerance. Since this chapter could be a book on its own, the reader is referred to relevant references at each stage, so that both neophyte and clinical practitioner can benefit from these pages.