In the past decade, modifications in HCT management and supportive care have resulted in changes in recommendations for the prevention of infection in HCT patients. These changes are fueled by new antimicrobial agents, increased knowledge of immune reconstitution, and expanded conditioning regimens and patient populations eligible for HCT. Despite these advances, infection is reported as the primary cause of death in 8% of autologous HCT patients and 17% to 20% of allogeneic HCT recipients . The major changes in this document, including changes in recommendation ratings, are summarized here. The organization of this document is similar to the previous guidelines. Specifically, the prevention of exposure and disease among pediatric and adult autologous and allogeneic HCT recipients is discussed. The current recommendations consider myeloablative (MA) conditioning and RIC for allogeneic HCT similarly, because data on infectious complications following RIC compared to MA conditioning are sparse [4-7]. However, increased information regarding posttransplant immune recovery highlighting differences between MA and RIC HCT are included. The sections of the document have been rearranged in an attempt to follow the time course of potential infectious risks for patients receiving HCT. Following the background section, information on hematopoietic cell product safety is provided. The subsequent sections discuss prevention of infection by specific microorganisms. Following organism-specific information, the sections then discuss means of preventing nosocomial infections as well as "dos and don'ts" for patients following discharge posttransplant. Finally, information on vaccinations is provided. This will hopefully allow the reader to follow the prevention practices needed from the time a donor is selected until the patient regains immune competence. Several topics are new or expanded from the prior document (Table 2). These include information on multiple organisms that were previously not discussed, but have seemingly become more clinically relevant in HCT patients over the past decade. Data, and where possible, recommendations, are provided regarding the following organisms that were not included in the previous document: Bordetella pertussis; the polyomaviruses BK and JC; hepatitis A, B, and C viruses (HAV, HBV, HCV); human herpesviruses (HHV) 6, 7, and 8; human metapneumovirus; human immunodeficiency virus (HIV); tuberculosis; nocardiosis; malaria; and leishmaniasis. In recognition of our global society, several organisms are discussed that may be limited to certain regions of the world. Included in that section are also those infections that may be ubiquitous but occur infrequently, such as Pneumocystis jiroveci and Nocardia. Several other changes should be noted. For bacterial infections, these guidelines now recommend quinolone prophylaxis for patients with neutropenia expected to last as least 7 days (BI). Additionally, the recommendations for contact precautions (AIII), vaccination (BI), and prophylaxis for patients with GVHD (AIII) against Streptococcus pneumoniae have been strengthened. The subsection on central line-associated blood stream infections is now in the bacterial section. The vaccination section has been dramatically expanded. Changes include the recommendations for pneumococcal conjugate vaccine (PCV) rather than polysaccharide vaccine (PPSV-23) for pneumococcal vaccination, starting some vaccinations earlier posttransplant, and the addition of recommendations for Varivax, HPV vaccine, and (the nonuse of) Zostavax vaccine are included. Two additional appendices were added to provide information on desensitization to sulfa drugs and visitor screening questionnaires. Finally, the dosing appendix has merged both adult and pediatric dosing, and provides recommendations for several newer antimicrobial agents that were not previously available. In summary, the changes and expansion to this document reflect the growing body of literature detailing infectious complications in HCT patients.