The care of the newborn unlike other areas of medicine affects the care of a changing and expanding patient population. Advances in medicine have made it possible for very small infants to be able to survive and have productive lives, but the challenge for neonatologists caring for these small infants, is ever greater. This edition of our book is intended to serve as a reference for neonatologists regarding hematologic problems of the newborn. It is intended to be a practical guide, a “how to book” yet provide the scientific bases and understanding of the problems when possible so that we can make decisions based on evidence. We have assembled a group of authors both neonatologist and hematologist that have made hematologic problems of the newborn their focus and passion as well as physicians expert in neurology, oncology, immunology, infectious diseases and transfusion medicine. Our mentors Gerald Rothstein and Frank Oski helped us develop a passion for the field of neonatal hematology. Dr. J. Lawrence Naiman who co-edited the book Hematological Problems in the Newborn with Dr. Oski has been an inspiration for us and always helpful with editorial comments and support throughout the previous edition and the current one. We have divided the book into sections of developmental hematology that provides the understanding of the physiology of blood, red cell, platelet, leukocyte, immune, and hemostatic disorders and a miscellaneous section including transfusion therapy, oncology, fetomaternal interaction and reference values for the newborn. We hope this makes the book easy to use and practical. We are fortunate to have assembled a group of experts in the field that have contributed to the knowledge of neonatal hematology. We thank them and their families for the time they have devoted to the production of this book and their patience with the three of us and innumerable emails. We are thankful to Dr. James A. Stockman, III for writing the forward to this edition, his advice and mentorship throughout the years. Lastly we would like to thank our families whose activities have been limited by our efforts to write this book specially our wives (Wendy, Alice and Jill) our children, their partners and our grandchildren (Alessandro and Katie, Tessa and Travis, Lucas, Audrey, Jacob, Abby, Andrew, and Henry, Elsa, Ansel, Louisa, Atticus, and Cosette) without their understanding we could never had completed this text.