This text provides a comprehensive, up-to-date review of chimerism. The first part of the volume presents the causes of chimerism, specifically focusing on fertilization and early embryonic errors, pregnancy and multiple gestations, and transplantation and transfusion. The second part of the volume outlines clinical identification and consequences of chimerism. Chapters in this section focus on the effects of chimerism on testing in relationship determination and forensics, prenatal genetic testing and screening, and blood and HLA typing. This part also reviews new data concerning matching donors and recipients for transplantation, while outlining the risks of transplantation, such as graft-vs-host disease and passenger lymphocyte syndrome. Additionally, evidence on the role of chimerism in autoimmune disease and cancer is presented.