Book excerpt: This book, written by a team of international experts, concisely reviews the rationale and clinical application of image-guided total marrow irradiation, a rapidly emerging area in radiation oncology and hematopoietic cell transplantation. The aim is to provide the practicing radiation oncologist, hematologist, medical physicist, and bone marrow transplant researcher with a fundamental understanding of key aspects and an appreciation of the increasing significance of total marrow irradiation as conditioning for bone marrow transplantation. Detailed attention is paid to the impacts of recent advances in radiation therapy technology, functional PET and MRI, and understanding of the response of bone marrow to radiation. Full consideration is also given to the ways in which technological advances in image-guided radiation therapy have created new opportunities to treat bone marrow transplant patients with limited transplant options due to advanced disease, age, or co-morbidities. Further topics covered include the ways in which cancer stem cells and the marrow microenvironment influence response to radiation therapy and the implementation of new-generation predictive radiobiologic factors in the clinic.