Organ transplantation is now the treatment of choice for many end-stage diseases. However, the gap between organ demand and donor availability has progressively widened, and the severe shortage of organs for transplantation has resulted in the increasing use of expanded donor criteria, allowing the inclusion of older donors as well as donors with mild disease. Thus, organ donation may involve the risk of the transmittal of unwanted host factors, such as infections and malignancies. Infectious microbes and unexpected diseases that are present in an organ donor have the potential to be transmitted to the transplant recipient. Although the transmission of donor-derived infectious diseases was reported to occur in less than 1% of all donations from deceased donors, significant morbidity and mortality can occur following such disease transmissions. Infectious diseases remain a major complication in solid organ transplantation, and the study of donor-derived infections is an evolving field. Despite recent improvements in the microbiological screening of donors and detailed reviews of potential donors’ medical records, persistent clusters of donor-derived infections in transplant recipients remain. Bacterial, viral, fungal, parasitic, and other rare infections can be transmitted through organs and tissue allografts. However, the transmission of microorganisms from allografts is not likely to cause infectious complications in every transplant recipient. The risk of infection is mostly related to the recipient’s net state of immunosuppression. The balance between the recipient’s state of immunosuppression and epidemiological exposures contribute to the risk of infection (Fishman, 2007; Fishman & Rubin, 1998). Immunosuppression not only increases the risk of tissue invasion, dissemination, and superinfection, but also blunts the typical inflammatory responses that alert clinicians to the presence of infection after exposure. As a result, the recognition of infection is more difficult in transplant recipients than in individuals with normal immunities. The presentations of infections are often complicated by noninfectious events, such as allograft rejection. Specifically, 40% of infections in liver transplant recipients were not associated with fever (Chang et al., 1998). Thus, intervention treatments of infections may be delayed. The goals of patient care after organ transplantation are to prevent the transmission of donor-derived infections, to recognize the presence of infections in solid-organ transplant recipients, and to intervene early when such infections occur. In addition, malignancies that are transmitted from the donor due to direct transmission of tumors or to tumors arising in cells of donor origin can also occur in organ transplantation. For example, melanoma, which is one of the most frequently reported and lethal donor- derived malignancies, has a high transmission rate. Therefore, potential organ donors should be carefully screened for histories of malignancies.