This chapter presents discussion on infections in transplant recipients. Infections are a major cause of morbidity and mortality in transplant recipients. Solid-organ transplants (SOT) include those of the kidney, liver, pancreases, heart, lungs and intestine. Long-term success for SOT patients varies according to the type of organ transplanted, the number of organs transplanted simultaneously and the type of disease that caused the organ to fail. Hematopoietic stem cell transplantation (HSCT) involves the intravenous infusion of autologous or allogeneic stem cells collected from bone marrow, peripheral blood or umbilical cord blood to re-establish hematopoietic function in patients whose bone marrow or immune system is damaged or defective. Infections, pathogens, antirejection drugs, parasitic infections, and prevention of infection in transplant recipient are the topics which are covered throughout the chapter.