Donor chimerism testing has long been a valuable tool to assess the status of engraftment in recepients of allogeneic bone marrow transplant. This book is based on my dissertation on donor chimerism testing in patients of aplastic anaemia and beta thalassaemia following allo-BMT and current published material available on donor chimerism. I hope that this book guides haematologists and laboratory technologists in how to assess this important parameter in post transplant recepients.